Assalamu alaikum. My name is hasan. I live in Italy. I go to an Italian school and I want to invite my Christian friends to convert in Muslims. They believe only in god but not in religions.what I can do for invite them all in islam ?

Wa aleikumus-Salaam, my beloved brother. I`m surprised no-one has given you an answer. First of all, pray 2 rak`aat nafl and make du`aa for Allaah to first guide them to Islam, then to Sunnah, then to give them thabaat (that they never turn back.
You can then e.g. ask them to go to www.all-quran.com when they`re alone and peacefull, and not doing anything else to listen, and then tell you what they felt, because you believe it`s a miracluous Revelation from The Creator of the universe to man. So He Himself has sent Messengers -last of them Muhammad (sAaws)- all teaching us Who is He, and what is His Religion, and how to worship Him. If they agree, then inform them that He created us and is taking care of us, and our purpose in this world is to worship Him Alone, and everyone wants to worship something, but people are confused as to who, and how. Then call them first to accept shahadah, then salat. etc. Ask them simply sometimes come to mosque. Be always clean, truthful, and kind. Salaam.

Tell them it`s no use not to be ready to follow the guidance of God, because He only guides to what is best for us, and He knows better than we. And if they believe in Him, then it`s easy, because just they need to be sincere and ask Him to establish the Truth wihtin their hearts, and give them certainty from Himself.