Sometimes comparing languages with each other and with their ancestors helps to understand and accept the complications of a single language you are trying to learn. I think this may be one of these cases. I will show you how German main clause word order differs from the English one in just two fundamental details. This tells you exactly where you intuitions from English break down when trying to apply them to German.
Word order of Proto-Germanic, a reconstructed common ancestor of all Germanic languages (including German and English) was SOV, i.e. subject - object - verb. This was also originally the preferred word order of Proto-Indoeuropean and is the preferred word order of Latin, classical Greek, Sanskrit and many other languages in which a strong case system makes word order less important.
The general trend in Germanic languages (even more generally in European languages) is that SOV word order gradually evolves into SVO word order, going through a tricky intermediate stage known as V2, meaning "verb second". In English, this process has almost completed, though not completely:
Did you know that questions in English still have a form of V2 word order?
Rarely will you encounter other English sentences, such as this one, which also still have V2 word order.
In the previous two sentences, the subject "you" was placed between the conjugated verb ("did"/"will") and the remainder of the verb group ("know"/"encounter").
V2 word order is tricky, and that's precisely because of its nature as an intermediate stage between SOV and SVO. The most important complication is that very often it's not the entire verb group that comes in second position, but only a single word: the conjugated verb. The remainder of the verb group (if there is a remainder) comes at the end of the sentence.
(Note that V2 is not a single system but just a label for a family of word order systems. The fine print varies by language. The same is true for SVO and SOV as well.)
In your example, the verb group is "holen können" ("be able to pick up"), or in conjugated form "[du] kannst holen" ("[you] can pick up"). As it consists of more than one word, in V2 word order it must be split. Since English also still has some remnants of V2 word order, you can use it to get an instant though partial intuition for what's going on.
For sentences without an object, in both languages the normal word order is SV:
Du kannst holen = You can pick up
However, the rule in V2 word order is not that the subject comes before the verb. The rule is that the most important part of the sentence comes first (or by default the subject), then the conjugated verb in second position (except if it came first, of course), then the subject (except if it came first, which is the usual case), and then the remainder of the verb group (if any).
If we add a qualification such as "selten" ("rarely") and place it first, as the most important part of the sentence, then in English we can form the sentence in V2 word order, and in German we must do so:
[no German equivalent] = Rarely he can pick up. (SV[O])
Selten kannst du holen. = Rarely can you pick up. (V2)
In yes/no questions, by convention the conjugated verb is the most important part of the sentence and therefore comes first. In this case, even in English we do not have a choice but must use V2 word order:
Kannst du holen? = Can you pick up?
So we have the most important word kann (can), then the subject du (you), and then the remainder of the verb group holen (pick up).
Now comes the really tricky bit. If there is an object as well, the English and German forms of V2 put it in different positions. English, which is already quite close to SVO, puts the object right after the remainder of the verb group. In German, however, the object appears just before the remainder of the verb group because the German rule says that the remainder of the verb group comes at the very end (where it was in SOV).
Selten kannst du den Beamer holen. = Rarely can you pick up the beamer.
Kannst du den Beamer holen? = Can you pick up the beamer?
Saying "Kannst du holen den Beamer?" in German is just as wrong as "Can you the beamer pick up?" is in English. In fact, it's more acceptable to say "Kannst den Beamer du holen?" or "Can the beamer you pick up?". Though weird in prose, these are word orders that can actually occur in poetry.
And now we come to the really annoying bit. As we have seen, German word order differs from English word order in two major ways:
- In German, all main clauses have V2 word order. In English, this phenomenon is restricted to questions and (optionally!) to sentences that start with an emphasized word that is not the subject.
- In German V2, not only the subject can split the verb group, but the object can do so as well.
The annoying bit is the following consequence: In a German sentence, even if the subject comes first, hence does not split the verb group, the object can still do so!
Du kannst den Beamer holen. = You can pick up the beamer.
In this example, the English sentence is in SVO order, though we could also say that it's in V2 order, which amounts to the same thing if the subject comes first anyway (hence can't split the verb group).
But the German sentence is definitely in V2 order. As is the case by default even in V2, the subject du comes first. Then we have the conjugated verb kannst. Then comes the object den Beamer, splitting the verb group. And only then follows the remainder of the verb group, which is holen.
Again, in German this is absolutely not optional. If you use SVO word order and say "Du kannst holen den Beamer", you will obviously be understood, but people are likely to correct you because it's just wrong.
Now you may ask: Why does German have these unnecessary complications compared to English, and how do German speakers cope with them? The above should have shown you that even English word order has some weird complications of a similar nature. English was once as bad as German is now, but it has progressed faster towards SVO word order. German is basically moving on the same path, but is slower. And splitting the verb group with an object comes as naturally to native German speakers as splitting the verb group of a question with the subject probably comes to you.
PS: Apparently what I called German V2 is actually V2 + something called the sentence bracket. See RHa's comment if you want to understand the correct terminology.