ok a few things to put out here. i'm a lvl 55 bstmaster and i'll tell you how it works. First of all, this is an extremely frustrating job. You will die so many times it isn't funny. heck i died 7 times right after getting lvl 55, luckly i had a good buffer up or i would have de-lvled.

Charming - Charming works on almost all the mobs in FFXI, with the exception of a few. you can't charm beastmen, you can't charm ochu classes, I.E. overgrown rose and marlboros, and you can't charm Notorious monsters. there are a few others, and there is no exception to this rule.

The duration of charm is variable to your lvl vs the mobs lvl your trying to charm. a charm will hold on an even match mob for about 3 min. long enough for most any fight you'll have to do. DC lasts for about 5-6 min, and so on. you can keep a too weak charmed for a long time. although IT mobs only stay charmed for a few seconds.

Exping - while exping, it is quite simple how it works. you simply grab an even match mob to use as a pet, and fight alongside your pet. Beastmasters are masters of hate control. there is a very thin line on how well your pet holds hate. one extra cure, or one hit too many, and you'll take a pop in the face. the line for bsts is so much smaller than a regular exp parties. in fact most bsts don't even start fighting with thier pet until lvl 35. you have 3 main subjobs that are used while soloing. in order of greatness whm-rdm-nin. whm gives you the least amount of downtime while lvling. with divine seal + CureIII your up and ready to go in no time.

party/duo/trio - a few bsts like to party all of the time. while this may seem like an easy route, i do not recomend it at all. bsts that party CAN NOT SOLO. they are absolutly horrible at soloing. i know a lvl 75 bst, and while he's been playing the job longer than i have, i can solo circles around him because all he does is party. Duo's and Trio's are good for getting past rough lvls. some lvls the exp just plain sucks. i tend to stay away from duo's and trios as best i can.

Abilities - your two hour will save your life. some think it's useless, but when you have a scorpion running you into the ground, and it's IT so the charm isn't going to last at all, you can just two hour it. it makes your pet stronger, and it WILL stay charmed for at least a half an hour.

Leave is your best friend by far. it allows you to release your pet at any time you wish. this allowes you to get full exp for your kills, and allowes you to save yourself when you have 6 crawlers breathing down your neck.