do i need to charge my iphone before using it

No, there is no need to charge it first. Unless, of course, it doesn't have any charge on it. With lithium ion batteries, there's no need to fully charge them before use, drain them completely or any of the things one needed to do with older types of batteries.

Apple does recommend letting the device drain until it turns itself off once month and then fully charge. However, that's just to calibrate the battery sensor, making the indicator more accurate. It doesn't affect the life of the battery.

The best practice is to fully charge it first, but it probably won't hurt it if you don't.