A collocation is when two or more words link together and form an expression.
Perhaps
the biggest problem with collocation is that there no rules and reasons
why. However, using collocation appropriately is one of the strongest
signals of fluency so it is well worth studying.
If you click here you will be taken to a dictionary which gives you words that collocate with any word you choose.
This page has a selection of collocation exercises. Do not try and work through them all at once.