Hesitates and then jumps into gear

This summer, my 2000 Subaru Legacy Sedan started to hesitate when I try to accelerate from a complete stop (at least this is how it started). It basically just sits there and then jumps into gear. I push the gas and nothing happens for a few seconds. The other day, I reversed out of my driveway and when i put it into drive, it wouldn't go. I was pushing on the accelerator, and it just revved. I switched back to reverse and it went fine, but it took a bit of effort once I switched back to drive for it to go. I didn't want to push too hard on the accelerator in case it jumped forward and into one of my neighbors' cars. Any help with this would be greatly appreciated. I just want to know what I may be dealing with before I take it into the shop.