I am learning objective-c my basic purpose if to development a msging client, please suggest me good site for lessons and help. Thanks.
W3schools.com will be better for you.
You need a Jabber / XMPP server to host your chat. You need a XMPP client library like XMPPFramework. I recommend that you learn objective C properly before starting with this application as its more complex than simple forms and stuff. I made a variant using just a web server. I had to code PHP to recieve messages and push it back to the app continously and it ended up being a pain for the server as well as the app as it kept polling. I would recommend that you use an XMPP Server as I mentioned (preferabbly install ejabberd on your mac) and then build the app around it. Use apple push notifs to query the server and keep users updated. Hope this helps
For lessons I recommend you download videos from Lynda (you can buy it) or if you could get it off p2p networks as well (if you know what I mean). I personally like this iOS 7 tutorial that recently came out. Really neat and better when compared to lynda (and that's my opinion)