I'm going to try to be as polite as possible, because this is obviously a question that...well...someone who has the mental capacity of a gold fish would ask, so here we go. Basically, the achievements which you are refering, can only be obtained in a FFA (Free-for-all) playlist. Which means you're most likely going to need to play some Lone Wolves. To select the Lone Wolves "URL" (For future refernce, this is called a playlist) you must go to matchmaking, and select the playlist from the Ranked subsection. At this point, you can click the start game button. If these weren't detailed enough, try looking at the guide book that came with your Halo 3 disc, that should tell you how. NOTE : You must have a working internet connection, and be subscribed to Xbox Live with a GOLD account.