At what lvl can rangers use spells??

I honestly used to know that. I think its in the mid teens level's, but, nonetheless, it only becomes available much later in BG2.

at lvl 8 they start by getting 1 lvl 1 spell

Both of the above replies are right. Rangers start getting their Druid spells at LEvel 8, and they don't get them until BG2. Even though Rangers can reach Level 8 with ToSC, their spells simply weren't implemented in BG1--gotta wait until BG2.

Spoiler!!
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Just realized, the spells I was thinking of are the mage spells that come available to rangers. When you reach like level 12 you get 3 or 4 mage spells.

No.

Rangers get Druid spells. In BG2, there is a Ranger kit called the Stalker that adds 3, count 'em, THREE Wizard spells to your Priest Scroll (Haste, Protection from Normal Missiles, and Minor Spell Turning, if I remember correctly), but that is the only way Rangers can ever cast Wizard spells.