Vi øver på bakoverpadlingen og styretaket.

In Norwegian, å øve på noe is the usual way to say to practice something.

• Vi øver = We are practicing / rehearsing
• Vi øver på bakoverpadlingen = We are practicing backward paddling

So på is part of the normal pattern here. English does not need a preposition in the same way, but Norwegian often does.

Øver is the present tense of å øve.

A useful thing for English speakers: Norwegian verbs do not change for different persons.

• jeg øver
• du øver
• vi øver

So the same present-tense form works with all subjects.

Because Norwegian usually writes compound nouns as one word.

So:

• bakover + padling = bakoverpadling
• styre + tak = styretak

This is very common in Norwegian. Where English often uses two words or a hyphen, Norwegian often prefers one compound word.

Those are definite singular endings, like the in English.

• bakoverpadlingen = the backward paddling
• styretaket = the steering stroke

The ending depends on the noun’s gender:

• en padling → padlingen
• et tak → taket

In compound nouns, the last part decides the gender and the ending.

Yes, you could. That would sound a bit more general.

• bakoverpadling og styretak = backward paddling and steering strokes/techniques in general
• bakoverpadlingen og styretaket = the specific techniques/strokes being practiced in this context

In real usage, both can be possible, depending on whether the speaker means the techniques in general or particular ones already understood from the situation.

It is made of:

• bakover = backward / backwards
• padling = paddling

So bakoverpadling is backward paddling, and bakoverpadlingen is the backward paddling.

It is made of:

• styre = to steer
• tak = stroke / pull / paddle stroke

In paddling language, tak often means a single stroke or paddle movement. So styretak is a steering stroke, and styretaket is the steering stroke.

No, it is a very normal Norwegian main clause:

• Vi = subject
• øver = verb
• på bakoverpadlingen og styretaket = prepositional phrase

So the structure is simply:

Subject + verb + rest

A related point: in Norwegian main clauses, the finite verb normally stays in second position. For example:

• I dag øver vi på bakoverpadlingen og styretaket.

Here I dag comes first, so øver still has to come second.

Because both nouns belong to the same phrase after på:

• på bakoverpadlingen og styretaket

This works just like English on X and Y or with X and Y. You do not need to repeat the preposition before the second noun unless you want special emphasis or a different structure.