First go to chapter 1 level 12 near the middle of the level you will find a part that looks like this
then you got to climb up and you will get your first achievement and 11 coins


Second go to chapter 3 level 13 go right near the end till you find this
you want to climb up the right side and once done you will get your last achievement and you will be greeted with a unique rank skin
last but not least if your new to the game and dont know how to equip these skins you will need to go to inventory skins and click specials as seen here
hope this helped you guys. ps: this is my 1st guide sorry for the bad positioning with pictures and stuff