“mo ii desu” (can do something) and “wa ikemasen” (cannot or not allow to do something). You have to use ~te form for the verbs just before the above sentences. Rules : Verbs (~te form) + “mo ii desu” or “wa ikemasen”

Q : Can I smoke cigarrette? – Tabako o (suu)sutte mo ii desu ka?
A : Yes, you can smoke cigarette – Hai, Tabako o sutte mo ii desu (Positive)
A : No, you cannot smoke cigarette – Iie, Tabako o sutte wa ikemasen
Meaning : Tabako (Cigarrette), Suu (Smoke)

You can stop your car – Kuruma o (tomeru)tomete mo ii desu
Can I go back now – Ima, (kaeru)kaete mo ii desu ka

Form a sentence in English and try to use the above sentences.