The simplest answer is that if you use what's called a modal verb (need, want, may, can, should, etc.) and then follow it with a second verb, the second one needs to be in infinitive form.
For example:
Gusto mo bang lumabas ngayong gabi? (Would you like to go out tonight?)
Dapat kong gawin ito. (I should do this.)
Kailangan nating dagdagan ang Tang. (We need to add more Tang.)
Pwede ba naming pumunta sa mall? (May we go to the mall?)
Nais kitang pakasalan. (I would like to marry you.)
Ano'ng ibig mong sabihin? (What do you mean? Literally "What do you want to say?")