Learn Polish: Czy autobusy kursują tu często? - Do buses run frequently here?

In English, a bus 'runs', but in Polish, biegać is strictly for physical running with legs. For public transport operating on a regular schedule or route, Polish uses the specific verb kursować. You could also use jeżdżą (go/drive regularly), but kursują is the most precise word for scheduled transit.

Since this lesson is about 'every' (co), how would I answer this question by saying 'They run every ten minutes'?

You would say Kursują co dziesięć minut. The word co means 'every' in this context. The number dziesięć stays in the nominative, and it forces the noun minuta into the genitive plural (minut), just like it normally would.

Is there a difference between tu and tutaj in this sentence?

No, tu and tutaj both mean 'here' and are completely interchangeable. Tu is just a shorter, slightly more conversational form that flows very well in the middle of a sentence like this.

Why does autobusy end in -y?