Learn Portuguese (Portugal): Tu pedes ajuda à professora.

In Portuguese, the verb pedir means "to ask for" or "to request". The concept of "for" is already built into the verb, so you just say pedir ajuda (literally "to request help"). Adding a direct translation for "for" would be incorrect here.

Could I use the verb perguntar instead of pedir in this sentence?

No, because perguntar specifically means "to ask a question" to get an answer or information. When you want to request a thing or an action, like asking for help, a favor, or a coffee, you must always use pedir.

Why do we use à before professora?

In English, you ask a person for something. In Portuguese, the structure is like saying "you request help TO the person". The word à with the grave accent is a mandatory contraction of the preposition a (to) and the feminine definite article a (the).

Is pedes a regular verb form?

It comes from the verb pedir. The tu pedes form follows the regular pattern, but pedir is an irregular verb overall. The trickiest part that you will see at this level is the "I" form, which completely changes to eu peço.