For agility you can have a sit, down or stand stay. A stand is the least secure stay, its easier for the dog to move, but anything that works for you and your dog.
Personally I dont use a 'stay' command - it isnt needed. You ask your dog into the position then teach them that they stay in that position until they are asked to do something else.
Teaching that is actually really easy - get them in position, reward, reward, reward then release them from the position. Then same again with a slight gap between rewards. (I will make a video of this when it stops raining)
Build up difficulty slowly, if your dog moves dont get angry with them (anger can actually make them insecure and want to creep towards you) you just made it too difficult - so put them back in position and start again making it nice and easy.
Once your stay is nice you can work on sometimes releasing them to you at a distance. Face away from them and call over one shoulder - have a treat or toy in that hand and hopefully they will run to that side.
Then you can add in a post turn, when they are running to your hand turn so they wrap around your body then chuck the toy/treat as the reward.
Dont forget to keep up the circle work as well :) (I dont ask for much eh? :D )
make it all FUN (for both of you) and better to do a couple of 1 min training times rather than trying 1 10 min boring training time