can someone tell me how do these things work? you get them from fortresses and put them on braclets but how do they work? cooldowns , increases , durations and etc?

afaik the talismans are like shadow items, have betwen 60/120 mana points, then dissappear. at least those ones you buy at the giran jewelery shop.
imo this talisman are like tattos in c4 (miss those times :/ ) they can improve your speed, critical attack, mana regeneration, etc.

Thats all i know, i dunno how it works on retail, i play in some shi7ty l2j server.

you have 2 types of talismans
1 gives sort of passive skill like increase run speek, attack speed, matk and so on
the other is a skill type talisman wich appear in your skill list
talismans have mana
each mana point is consumed each minutes while you have your talisman on your bracelet.

all talisman with active skills burn also mana points each time u use the skill.
of corse, talisman's skills are better than passive ones in power
low grade passive talisman increase speed gives you 2 speed points
active one gives you 5 points (both low grade)
talismans have also grade and type depending the color they have
red/yellow/blue/white/dark
talisman's skills stack with normal buff, i got a bless the shield talisman skill from fortress and it stack with normal bless the shield
some skills are also talisman specific, i got a talisman that regenerate all my HP/MP but it consume a lot of mana so the talisman was just able to use the skill 3 times.

and how much do they cost?

from fortress/castle : 10 epaulettes, you got one randomly
you can buy low grade talisman for around 2k at giran's grocery
yo can buy some from fame manager at rune or aden for 500 fame points