How i invite my friend?

ask him politely

No, i have an account here. I want to invite him.

Does he have Dota 2?

"Dear friend of mine, I would like to invite you to a glorious website known as "steamgifts"! It is a place of wonder and videogames, and you may reach this mystical land of generosity by going up to thy address bar, and typing in www.steamgifts.com"

Its not necessary invites anymore?

sure you are following all safety protocols. !

Go outside in a wide area, start a small fire. Then make sure it gives off enough smoke. Google up morse code or fire signal code. Then ask your friend to go outside and watch the sky in your general direction. You can then start the message. Tell him to buy some games on his steam account and register.