for jump & run games you can have a look at these 2 sample games:
1.) OneMoreLevel – You can use this demo as a starting point for the movement and collision detection of Super Mario like game mechanics
2.) StackTheBoxWithEditor – I would use this demo as a starting point to learn about the V-Play level editor, which can be used to create the levels. You can even let your players then create their own levels if you want. Furhter docs about how to add the level editor to your game are available here.