I think the biggest problem of understanding German sentences is the problem of...
In German it happens very often, that parts of a sentence, that logically belong together are spread wide across a sentence:
"to spend money" is in German "Geld ausgeben". "Ausgeben" is a separable verb, who's components "aus" and "geben" can be separated by miles of other stuff in the sentence:
Gerda gab gestern Nachmittag, als sie kurz vor Ladenschluss in dem großen Supermarkt in der Heinestraße die erforderlichen Lebensmittel für sie und ihre Familie einkaufte, 57 Euro aus.
Yesterday afternoon, short before closing time, when Gerda bought the required foods for her and her family in the big supermarket in the Heinestraße, she spent 57 Euro.
supporting clauses can split main clauses
A supporting clause can stand before, after and in the middle of the sentence that it supports. But also a supporting clause can be interrupted by another supporting clause. Sentences like this example with three insertions (which makes in sum four encapsulated sentences) are very rare, but grammatically correct:
Das Haus, in dem Karl, welcher die Schwester von Georg, der mein Arbeitskollege ist, geheiratet hat, wohnt, brennt.
As the english translation shows, this is also possible in english, but not in such an excessive way as in German:
The house, in which Karl lives, who married the sister of George, who is my colleague, is burning.
Mark Twain, when he learned German, had similar problems. In hie really great essay "The Awful German Language" he wrote:
There are ten parts of speech, and they are all troublesome. An average sentence, in a German newspaper, is a sublime and impressive curiosity; it occupies a quarter of a column; it contains all the ten parts of speech—not in regular order, but mixed; it is built mainly of compound words constructed by the writer on the spot, and not to be found in any dictionary — six or seven words compacted into one, without joint or seam — that is, without hyphens; it treats of fourteen or fifteen different subjects, each enclosed in a parenthesis of its own, with here and there extra parentheses, which re-enclose three or four of the minor parentheses, making pens with pens; finally, all the parentheses and re-parentheses are massed together between a couple of king-parentheses, one of which is placed in the first line of the majestic sentence and the other in the middle of the last line of it — after which comes the verb, and you find out for the first time what the man has been talking about; and after the verb — merely by way of ornament, as far as I can make out, — the writer shovels in “haben sind gewesen gehabt haben geworden sein”, or words to that effect, and the monument is finished.
The Awful German Language by Mark Twain, also available as free public domain audio-book