I am fairly new to collecting I have some rare cards, but I am wanting to buy a bulk lot of cards or trade my cards for a number of cards so I can get some bulk to my collection. How or where is the best place to buy or trade peoples spare cards with them?
eBay is a good place, as long as you buy from a top-rated seller, and as long as you use PayPal, as you will have the recourse to be refunded if you do not get what you bought through eBay and you also have your information protected by using PayPal to pay.
PokeBeach and PokeGym also allow trading and selling of cards between members, but you should read their guidelines and rules for trading and selling before actually using their sites to trade, buy, or sell for the best experience and so you are less likely to get ripped off in a trade or when buying cards.
It all depends on what particular cards you are looking for. Older cards are going to be more difficult to obtain, so perhaps eBay may be the best place to pick up a batch of older sets.
However if you are looking for playable competitive cards for this current format (season) then you can purchase online from eBay, Koolkingdom, Amazon or go down to a local supermarket, Toys R US etc.