Shrouding is good for completing one single quest at whatever level you like (Slipgear's Gem, the DoDh charm, you can shroud up as a rogue, have a mage summon you a bunch of levi rings and complete the entire charm run in <1 hour start to finish. Great fun, actually, check it out on
THIS page). Other than that, I have yet to meet anyone in-game who actually uses shrouds.
Progression refers to two things; on a personal level, progression usually refers to your character's development, i.e. rise through the levels, better equipment, access to new zones etc., and the guild-level where you and your guild together completes certain tasks to gain access to each expansion's end zone. Plane of Time is one such end zone; to gain access to that zone you need about 20 'flags', which you and your guild win by spawning and killing the boss mob of a large number of zones in the Elemental Planes.
Maximum melee distance is the farthest you can be from a mob and still hit it. When you are NOT the main tank, you should generally speaking always be at maximum melee distance; you may avoid some of the tricks the mob has up it's sleeve, and you may be able to avoid taking aggro from the main tank.
Weight reduction (or just WR) bags; you can get 10% WR bags for 'free' in the Bazaar, or make them easily with tailoring at about 100. Go to the BAzar, search for 'token'. These tokens can be handed in to an NPC called Caerlyna (if I remember correctly) to get you bag (have an inventory slot open). But just by looking at the tokens, you can see how much WR each type gives. Some types can be handmade, some can be quested for, so once you have the names, ALT+Tab out of EQ and look them up here and on EQTraders.