I'm learning about the "Trennbare Verben" now. So far, I have learned that some prefixes are separated from the main verb, and that it should be put at the very end of the sentence. I have come across a list, which was titled "Trennbar sind". Some of the verbs are:
Now, when we use "abfahren", we separate the verb.
Er fährt ... ab.
However, the verbs "weggehen" and "umsteigen" are not separated when used in a sentence, although they come under the "separable verbs" category. Why is that? And how do I know if the prefix should be put at the end of the sentence or not?