Welcome to all
Unfortunately for new people, there are not that many new players to the game, and it is tough to find groups. I recommend new players to start on classic servers (Ector, Lamorak and Gareth) b/c those servers are only a little over a year old and there are more new/casual players there. This game is over 5 years old, and people know how to level fast. With powerleveling, toons can become 1-50 in 10 hours or so. It is actually ridiculous that this is allowed, but it is what it is, and it hurts the new player base that comes here with questions as yourselves have and can not find anyone to answer them.
Now, for the original poster, Realm abilities are "extras" that can be bought using Realm Skill Points. You get your first RSP at level 20, but after that, you will have to kill other players to advance your character. The PvP system in DAoC is great if that is your thing. For new people, start in the battlegrounds. At levels 20-24, you may enter Thidranki. Killing other players here gets you realm points, which in turn gets your realm skill points. The realm skill points can be used to by extra damage dealing abilities, extra stats (str, dex, qui for example) or other special abilities (some of which can only be purchased at level 40).
Master Levels are something from the Trials of Atlantis expansion. At level 40, you may begin them. They are mainly battlegroup steps, so a lot of people are needed, but again, completing a series of 10 steps gets you extra abilities..these abilities are things such as water breathing, speed warps, group cure disease, cure near sight, etc....some are very, very powerful.
The shame is the game caters to the older fan base, who has no desire to level characters through the long hard grind, and wants to do it quickly..however, new players are left standing alone. You can easily level yourself in task dungeons if you choose, but those are very boring. Try to find a decent guild. I know my guild has plenty of players that are always leveling up, at least past level 20. You may have to get to level 20 on your own more often than not. However, on classic servers (which do not have Master levels or artifacts), all characters must start at level 1, so there are no /level toons.
btw, I am on lancelot Alb if anyone needs some help/guild to join.