Pops decking and fencing are pretty easy, loads of stuff on you tube.
With decking the best way to go, if you are not handy, is to make your decking area the size of your decking board then you have less cutting, so if your board is 3m make your deck that size. If your decking is 150 mm wide make your decking a multiple of that, adding 5 mm gap between boards, so 20 boards =3m + 85mm for gaps, if my maths is correct lol.
The support timber must be pressure treated, obviously.