Pokemon Holofoil's, PRICING? and what are PSA's

[kkthxbai]

Hey guys, i was going through my collection and pulled out 11 pokemon holofoils from 1999 and I think about 2 from 2000.
Just wondering if someone can explain to me how to tell the difference between the series, and what are these PSA thing's on ebay selling for thousands.. what's so special about them.

Also finally, maybe a price on what i've got, and if anyone has the missing pieces I might buy. I think I got a rough idea of pricing already, just want to check with you guys.

Pic's are below, everything is mint with ultra pro sleeves;

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Cheers, guys. =]

 

[Ultimate TC]

There not selling that's what the guy wants for them and I'm guessing never sold one. The shadowless Charizard there were 2 types in base set I think the shadowless one was slightly rarer. I hope this helps Im not to good with earlier Pokemon cards mainly newer playable ones.