Whitelist means if the server admin(s) has added you to the server if he/she has then you will have acess to the server, if not then you may need to contact the server admin(s) then hopefully he/she will add you to his/her list of players. Hope this helps
P.S I enjoy Minecraft alot so heres the server (awesome) i play on (its cracked and theres free flying and theres 4 differnt worlds) IP: mc.atomiccraft.com