Fights are an intrinsic part of MUD, and you are bound to be attacked eventually, by The Land's resident creatures if not by the other players! It is important to decide quickly whether you stand a chance of winning or not. If you think you're bound to lose, it's best to leave the fight as soon as possible. The command to do this is FLEE, shortened to F. This makes you drop everything you were carrying, and moves you in a random direction. Since it may be that there isn't an exit in that direction and you could therefore remain in the room with your opponent (who may well attack again!), FLEE is best used in conjunction with a direction - OUT is a good one, since most rooms have an OUT exit. Hence, if in doubt, F O!
If you think you can win, or would like to risk it anyway, do nothing! Fights continue automatically in MUD, blow by blow, until either party dies or flees. The exact details of how a round of fighting proceeds are quite elaborate, but are based on your strength, dexterity and stamina. The higher your dexterity, the greater your chance of hitting your opponent. The higher your strength, the more damage you will do when you do hit. Your stamina is how much damage you can take, and when it falls to 0 or less, you die. When you are hit in a fight, you are told your remaining stamina as a fraction of your total, eg. (39/45) means it's 39 out of a maximum of 45.
Lots of players wait until their stamina gets close to 0, then FLEE. A good many of such players get killed, because the time between blows in fights is randomly determined and there's a fair chance another exchange will take place before your FLEE command takes effect! So leave a margin of error when you decide to flee, in case your opponent gets another blow in! The most common complaint received by MUSE is "my flee didn't work", which is regarded by the more experienced players as meaning "I didn't flee in time"...
There are many other commands related to fights, and although most are too specialised to mention here, there are three which merit a brief outline. If you are attacked and are carrying something you think you could use as a weapon, use the RETALIATE (or USE) command, eg. USE STICK. This will increase the damage you do when you land a blow. To find out how badly injured your opponent is, use LOOK, as in L ENID. You'll be given a description which, although vague, is good enough to tell you whether you're making an impression. Finally, the command sequence F O followed by QUIT is very popular because people don't want to hang around if they are low on stamina. However, if your opponent is quick you can be attacked again after the F O but before the QUIT has been performed. The command SUPERFLEE (or SF) combines the two. It costs more points to use, but at least you'll survive!