ok, i have just a few questions to ask.

1)what is the "keen" ability on a weapon?
2)im playing a cleric, and i have the magic and war domains. do i ever earn more?

i guess thats all i have for now, these two have been bugging me for quite some time. thanks in advance.

According to the manual under improved critical, keen states that it already doubles damage. If you have improved critical, you can then triple damage. It usually means a sharp/finely crafted item. As for the different magic domains, I think you stay under whatever sphere you are in. I do not play cleric, so can not answer that with 100 % confidence, but that is how it usually was in older D&D

A keen weapon doesn't double the damage, but doubles the threat range. For example, a scythe hits critical damage on a roll of 20. A keen scythe hits criticals on rolls of 19 and 20 (i.e. doubled). Improved critical doubles the threat range again, so the scythe would now hit criticals on rolls between 17 and 20.

Another example, a raper criticals on 18-20. Improved critical or a keen rapier makes this 15-20 and finally, improved critical with a keen rapier makes it 13-20.

Sorry not sure about the domains.