Setting up Shimano 105 gears.

I wonder if anyone would be kind enough to help me? I'm new to cycling and I'm having trouble with my gears set up. I've watched loads of video on YouTube but I'm still at a loss as to where to start. Most of the tutorials just show what are mainly just minor adjustments and therefore look easy. Basically, I suppose I've messed around with them so much that they are way out. Is there a idiots start to finish guide available on how to set up both front and rear derailleurs? Or do I just give in and take it to a bike shop and pay???? Thanks.