yeah thats how skills work.
You have skill gems.
3 colors. Blue, green, red.
Blue gems are int based. green dex, red str. Which means they have stat requirements as they level up. A blue gem will require int to equip at increasingly large amounts.
So any class can use any color gem, but must find a way to meet the stat requirement to equip it. Choosing to purposely NOT upgrade a gem is for this reason. Gear, and passives give stats.
Items.
Items then have colored sockets. in order to use a skill gem you need to equip it, into a correctly colored socket.
Support gems, and linked sockets.
Next, you will start seeing linked sockets on gear.
A circlet with two blue sockeets, that are linked for example.
Support gems modify how your skills work, when linked.
http://www.pathofexile.com/skills/supportgems
Usually they will increase the mana cost, in addition to their effect. Support gems also have a color. So, now you need to find an item that has the desired color combination fused for your desired skill combo.
(or make one via the fusing orbs, and chromatic recolor orbs)
I think you said ice witch? so a popular one for that is freezing pulse and lesser multiple projectiles.
Blue freezing pulse and green lesser multiple projectiles.
Lesser mutliple projectiles will make freeing pulse deal 30% less damage per, but fire off 3 shots in a shotgun blast. Result, super high short range aoe damage.
ATTACK vs SPELL. This was not clear in older versions, and one of the new things to the UI.
When you look at a skill gem, it will say what its qualifiers are.
Poison arrow for example. (aoe, attack, bow, chaos, duration) should say projectile too, but doesn't.
But we can see, its an attack. not a spell. Something that effects spells, wont effect it.
2 or more. You CAN link more then one support into a single skill. but not 2 of one kind.
http://www.pathofexile.com/skills/remoteskills
Totems, traps and mines.