An independent clause can stand on its own as a sentence and forms a complete thought. In other words, an independent clause is a full, complete sentence. These clauses will always contain at least one subject and verb. However, an independent clause can be simple or a little more complicated.
Explanation:
this app helps you to ask questions about something you don't know or answer other people's questions.
I don't think a correction is necessary. Both parts of the sentence are already in the present tense. Plus, the use of "us" in the beginning of the sentence indicates a personal attachment.
The fog is doing the same thing as a cat.
