In the first gym (Oreburgh City gym/Roark coal badge) is to hard for me..

Use grass and water attacks for the water and grass starters. If you choose the fire starter then it should learn mach punch at lvl 14 which is super effective. Only train you starter, and do it at the mine.

Get a budew and train it until it learns grass moves or
Find a water pokemon.

...It's too hard? ...Fine. All 3 starters you chose have an edge against him.
Piplup and Turtwig have an advantage against as it is, so just attack with water/grass attacks.
If you chose Chimchar, however, you might want to do one of the following:
-Catch a Budew, and level him up until he knows Mega Drain, and use that move against the gym.
-Level up Chimchar to level 14 to evolve him into Monferno and learn Mach Punch, and use that move against him.

Try using a psyhic type moves or water attacks.

The first thing you should do is if you chose chimchar, get him to monferno ASAP. Roark uses moves that up defense. So take out his Pokemon with a powerful move. If you chose turtwig, all you need to use is razor leaf or any other grass type attack.that should take him out nice and easy. Needless to say anything about piplup.

Hope this helps!

Hyrules_Hero

Well if you chose chimchar for your starter Pokemon train him up to level 14; he will evolve and will learn the move mach punch. If you didn't choose him for your starter... Get another fighting type pokemon... Then you should be right to beat him...
Hope it helped
Yours senserly
Blakequirk123