Learn Spanish (Spain): Ellos terminan de revisar el proyecto luego. - They will finish reviewing the project later.

In Spanish, the phrase to say you finish doing an action is terminar de followed by the infinitive form of a verb. You always need the preposition de to connect terminar to the action that is being finished.

The English translation says "reviewing", so why does the Spanish sentence use the infinitive revisar instead of an -ing form like revisando?

In English, we say "finish doing" with an -ing word (gerund). But in Spanish, verb phrases like terminar de always require the infinitive (the base form ending in -ar, -er, or -ir). That is why we use revisar.

The Spanish verb terminan is in the present tense, but the English translation says "will finish". Why?

In Spanish, it is very common to use the present tense to talk about future plans, as long as the context makes it clear. Here, the time word luego (later) tells us this will happen in the future, so the present tense terminan naturally translates to "will finish".

Does revisar mean "to revise" like when studying for a test?

It looks like "revise", but revisar usually means "to review", "to check", or "to inspect", like reviewing a project in this sentence. If you want to talk about revising for a test in Spain, you would use the verb repasar.