I have a 2-part question. I want to play with my friend on his world.
how do we connect it? and
is it possible for us to both play on his world if we use different wifi networks? (eg we live in different places)
You currently can only play multiplayer in pocket edition by using realms that cost money or through being on the same wifi.
You can do it by logging into Xbox Live. Add your friend in Xbox Live and you can now play using different WiFi!!!
If you both have an xbox live account, search for his gamertag in the Add Friends option. Then, whenever he is online and playing on his world, you will be able to join. However, you won't be able to do so if he is offline.