Learn Hardcore Korean: aebeuro gireul hwaginhaeyo.

-으로/로 is a particle that often means by / using / via / through (a means or method).
So 앱으로 = using an app / via an app.
Rule: use -으로 after most consonants (앱 ends in ㅂ), and -로 after a vowel or ㄹ.

Why is it 길을 and not 길이?

길을 uses the object marker -을/를 because 길 (road/route) is the thing being checked/confirmed.
길이 would mark 길 as the subject, which would change the structure and emphasis.

What exactly does 길 mean here—road, street, or route?

길 is flexible. In this kind of sentence it commonly means the way/route (how to get somewhere), not just a physical street name.
If you specifically mean “directions/route,” you’ll also often hear 길(을) 찾다 (find the way) or 경로를 확인하다 (check the route).

What is the dictionary form of 확인해요, and how is it formed?

The dictionary form is 확인하다 (to check/confirm).
It’s a 하다-verb, so it conjugates like: