Can you hit a vein/artery in im injection? what if theres tiny bubbles of air in the syringe, what would happen?

If you're shown proper technique and location (depends on medication, volume, etc), it's difficult to hit an artery or major vein. If you DON'T follow proper technique, then it's fully possible to hit an artery or vein. Air bubbles in an artery can cause air embolism (essentially a stroke). In a vein they may do similar, although not nearly as likely.