Oh ok :
1.First of all,if u are creating a race /dm/dd map you need to add ''race'' in definitions :
http://wiki.multitheftauto.com/wiki/File:Editor_Definitions.png (there you have a pic how ''definitons'' looks) .You need to click there and to add race.Also click the Map Settings button in the top menu, go to the Gamemodes tab and add any gamemodes that your map is to be used with.(in your case that is race)
-When u finish first step then put your mouse on the element menu in the lower left corner and roll the mousewheel in this menu to bring up custom elements.(like a nitro,repair,vehicle changer)
2.I think u shouldn't use it yet becouse i see you are amateur in the creating maps and first you should start to make smaller and simplier maps but if u want to use rcg u can find tut's and download link's on youtube Good luck.