Playing BG1. How do I tell how much damage a weapon I have equipped is doing so I can compare what I should be using? Is there some table in game that will change my damage done as i change weapons? I am running the 2 games together per link below if that matters. Thanks

https://www.gog.com/forum/baldurs_gate_series/newbie_guide_modding_bg1_if_you_buy_bg1_bg2_from_gog

I am pretty sure that, if you right click on an item, the item's description will appear, and toward the bottom, the damage and other properties of the weapon will be displayed.

I think you can find the information on the character sheet page (the one that shows your stats), but I'm not sure.

As for reading it, if, for example, the damage is listed as 1d6 + 1, that means that the game uses a pseudo-random number to simulate the rolling of a 6 sided die (in the table top game, such a die would actually be thrown), and then adds 1 to it. 2d4 would mean that the game rolls two 4 sided die (or, more precisely, simulates this with a pseudo-random number) and adds the results together.

(Note that weapon descriptions are only reliable for weapons that you can obtain through normal gameplay; weapons only obtainable through cheats or save editing are not guaranteed to have accurate descriptions, or even descriptions at all.)

You may also find these useful if you're trying to find more in-depth info.

http://baldursgate.wikia.com/wiki/Strength#Scores_table
http://baldursgate.wikia.com/wiki/Weapon_Proficiency

Damage is only one aspect on which a weapon should be chosen. There are lots of others - speed, enchantment level, special abilities, various monsters being resistant to various type of damage, etc.
You should be fine in BG1 with almost any weapon, though, so if that's your first run, don't need to overthink.

Allow me to take a shot at explaining.

The AD&D 2nd Edition table top role-playing game uses six different dice: 4-sided, 6-sided, 8-sided, 10-sided, 12-sided, and 20-sided. A 4-sided die yields a number between 1 and 4, a 6-sided die yields a number between 1 and 6, and so on.

As previously mentioned, right-clicking a weapon in the Inventory screen will display info on the weapon, including base damage.

A normal dagger does "1d4" base damage. This translates to rolling the 4-sided die ("d4") once, to produce a number between 1 and 4.

A normal bastard sword does "2d4" base damage. This translates to rolling the 4-sided die ("d4") twice, to produce a number between 2 and 8.

A magic Long Sword +1 does "1d8+1" base damage. This translates to rolling the 8-sided die ("d8") once and adding 1, to produce a number between 2 and 9.

On top of this, the game also factors in the damage bonus from the character's Strength, if any. See page 132 in the Icewind Dale manual for this table.

Also, certain magic items, spells, and/or character states (fatigue, maybe?) may also give bonuses or penalties to damage.

And if you score a "critical hit" against an enemy, then the damage is doubled. The "to hit" roll uses a 20-sided die, and a "critical hit" is when you score a "natural" (i.e. before modifiers) roll of 20. (I'm not sure if critical hits will double the base damage and other damage modifiers, or just the base damage.)

(Note that most helmets protect against critical hits, and certain enemies may be immune to critical hits.)

Also, a thief's backstab attack can double, triple, or quadruple damage, depending on the level of the thief. See page 17 in the Icewind Dale manual for details on how to backstab.

If this damage system seems hokey, keep in mind this game is using AD&D 2E rules. Although imho, the Character screen could display damage a little better, like it does THAC0.

Hope this helps!