The Sniper is a very late game hero, he needs a lots of farming to be efficient. He's considered 'easy to play' by a lot of people, but that's totally not true : Hard carries are the hardest heroes to play and because of that, when a Sniper is picked, everybody starts to think : "Oh ****, game is lost" or "Oh no, another useless Sniper". If played correctly and get some good farm/kills, the Sniper can become a real monster and you'll regain faith in people's heart.
Here comes a brief description of the Sniper's skills, they are quite easy to use (50% are passive) and are the main reason why he's so called an "easy hero" :
Active, does damage and slow over time to enemy heroes and structures in the area of effect.
This spell is quite useless in my opinion. Some may say that its useful for pushing lane and stuff, but it's not really in your interest to push a lane since it will put you in dangerous positions for farming and will increase your gank appeal meter. Don't max it until you have nothing else to max out.
Passive, gives you a chance to mini-bash plus bonus damage to your target.
Your core spell, Max it at lvl 7.
Take Aim :
Passive, increase your attack range, you will have a greater range than tower, the best range of the game. You will use it at your advantage.
Active and cast time, Deal a X-FAT amount of damage to your target. Try to use it on heroes that do not have health regen or that are out of your attack range. This spell reveal the target during the casting time.
Sniper if well as gang or team attack. He does large damage i short time, but he need tanker (in early game). You can try attack from the jungle, but if enemies are more than 2, you should wait for other players and gang them. Sniper with that build's OP in late game so you can kill a lot of opponent one time.