1. is there any way to install my apps wheter from store or apk in my sd card so that they dont consume internal storage?
You can go into the Android settings, Applications/Manage Applications, and then for each app where it's possible, click on "Move to SD card." That will free up some internal memory by moving
a portion of some apps, but not as much as you could gain from root-only methods like, Link2SD. You could try the built-in Android method, and if it doesn't create enough space for you, you could root.
It may be worth noting that once you're rooted you can install apps like Titanium Backup ("TBU") which allow you to backup your apps to your SD card and then quickly restore them along with their data/preference settings. This lets you store a large number of apps that you may only use on rare occasions but would like to have available for quick installation-- even when offline. For example, you might use Google Navigation 98% of the time for GPS-navigation (because you usually have a 3G/4G data connection) but you might want to keep a big, TBU-backed-up offline-GPS-navigation app (like OsmAnd Navigation) on your SD card a rare occasion when you're driving or hiking through a rural area with no 3G/4G service and no way to use online-only Google Navigation (and no way to download an offline GPS app).
2 . can i do it by rooting the phone?
Once rooted, you can implement root-only memory-expanding solutions, like Link2SD. It will gain you much more memory space for apps and data than simply using the built-in Android utility mentioned in #1 above. I wrote a tutorial for the LG Optimus S on Link2SD with pros & cons versus Data2EXT. Much of it is applicable.
Guide: How to effectively increase internal memory using Link2SD (w/ pros & cons vs. Data2EXT). - Android Forums at AndroidCentral.com
Often phone models with root methods also have custom-ROMs that remove the carrier's bloatware and free up some memory.
3.if i rooted it, can i unroot it?
There seems to be a rooting method for your phone. (See below.) Usually there is a return-to-stock method also but you'll have to look around the various forums. Though there's practically no reason to return it to stock since most warranties are like 30-days and the phone store employees don't care if you've rooted it.
http://forum.xda-developers.com/showthread.php?t=1137762