One of the spokes of the front wheel of my bicycle is removed and this really affected the alignment, How can I replace it and make the wheel balanced back, or do I have to replace the whole wheel?
You don't need a new wheel, and the repair is cheap if you have the correct tools.
Here's a guide if you want to try it yourself, or I reckon it would cost 0.5 - 1hr labour at a bike shop (plus the price of a single spoke).
edit - just read that it's the front wheel, which makes things easier still. No need to remove any cassettes!
Replacing a spoke is easy. Truing the wheel (that is, getting it straight) is harder - but it's a skill worth learning. If you want to learn, buy a new spoke and a spoke wrench; if you're pressed for time, have the shop fix it. Either way, there's no need to replace the wheel.