Put the carrier on your body, cross -body like a handbag. Remove the top so it doesn't get in the way. The wider part should be facing the back, this is where your dog's behind will go when sitting. Pick up your dog and just hold him/her for a few minutes. Slowly lower him into the carrier. The padded sides will feel like your arm and she will not even realize he is in a carrier, and will just think you are holding him. Sometimes they will stiffen their legs so they are standing in the bag but after a few minutes she should relax and you can gently direct her to sit.
If they are unable to reach their head out, you can either try a smaller size or put a small, rolled blanket or towel on the bottom of the carrier to boost them up. We also sell cushions for this purpose.
After a while they should relax enough so that they will curl up and you can put the cover on if needed.