I would first start off with easy spells. It depends on how well you are at the craft, and what you want to learn. Personally, I started off learning weather spells to practice on and got to the point where I didn't even need a spell to summon the sunshine. If you already have some experience, go on to the protection spells. Look for spells that wont have any negative consequences if cast incorrectly.
there is no spell you need to learn. i'm gonna assume you're wiccan, you don't need to cast spells. my friend follows the path and doesn't believe in magic. it doesn't mean she's not wiccan, it just means she doesn't cast. keep this in mind, please.
since you wish to learn, start slow. learn how to work with energy. charge and ground yourself. do this once a day for about a week, or until you get the hang of it. once you can do that, you can cast spells. myself, i began with candle magic. it can be as simple or complicated as you want, and all you really need is a candle, a match, and focus. be sure you visualize your desired result the whole time the candle burns, and let the candle burn out. if you are using a big candle and you don't want to sit for 2 hours [example] you can always break it up. do it eery night for 3 days until the full moon when the candle will burn out. or, you can snuff the candle [don't blow it out] and leave it as is, but you should then melt down the remaining candle [or bury it or whatever] because it has been used in a spell, and it has been charged for that one spell.