What's next for my apple tree?

I followed the "ehow" how to plant an apple tree. I've had it for a year now and it's over three feet, but under four and is supported with a stick to keep it growing straight. I use SuperSoil all purpose potting soil for my plant. It's also still in my house and I get annoyed because there are a LOT of tiny flies. So I am planning to put my plant outside, but I don't know the type of pests that will harm my tree sooo. I need some help. I live in southern California and my backyard is full of foxtail weeds. My ignorance caught up to me. I know nothing about gardening, any help?