Diablo 2? where to start

[Underskilled]

No matter where you start, playing online is your best bet. You can easily find those willing to run acts with you, and of course every once in a while go trolling for games of high levels giving away free stuff, and get your fill

[Dtloweca]

Mods enhance games but I would suggest beating the game once before you start modding.

[Annoying]

Roll what you want. Don't go for "easiest" or "best". Go for what looks cool. If you're playing single player, I wouldn't expect to be able to beat hell difficulty, but have fun with the quests and storylines. Don't go spoilin' it for yourself. =D

Quick runthrough so you can figure out what you want to play:
Amazon - Mad bow skills or mad javelin skills. Passives increase crits/dodges/etc... and allow decoy or valkyrie summoning as a pseudo permanent companion.
Assassin - Mad melee skills or mad trap skills. Shadow disciplines give you utility like a stun or a sprint. allows for summoning a mirror companion with skills equal to yours.
Necro - Mad summoning skills or mad poison/bone nuking skills. Curses do tons of crazy stuff. Enhance damage, slow enemies. Lots of debuffs, but only one at a time iirc.
Barbarian - Classic beat-em-up style. Melee skills can either be offensive or defensive oriented. Whirlwind is a load of fun =P. Warcries buff allies or debuff enemies rather well.
Sorceress - Classic nuke/mage. 3 elemental trees. Keep in mind that things in nightmare difficulty will be immune to an element sometimes, and in hell everything is immune to at least something. Expect to rely on your merc a ton after normal mode is over... lots of resists flying around.
Druid - Shape shifting melee skills, or mage-like nukes. Has summons for support/buffing.
Paladin - Physical brawler type combat or magical nuker type combat. Auras are huge and completely flexible. Fanatacism + Zeal is a great starter goal, as is Blessed Hammer+Concentration. Tons of options.

Good luck.