Start a singleplayer or multiplayer game.
Spawn the ragdolls or props that you'd like to have in the animation.
Choose the Selector tool from under the HAT Tools list:
Select the ragdolls or props you'd like in the animation.
Make sure that you've selected the props correctly. Opening up the HAT menu with your binded key will confirm that you've selected the prop by highlighting it with a green wireframe.
Pose your props to what you want.
Press the record button, which looks like a circle. This snapshots all of the selected props' positions and angles.
Add a new frame by pressing the "+" button, select the new frame by clicking on it (although it should already be selected), and then pose your prop again.
Notice that there is a ghost of the prop from the previous frame. If a ghost doesn't show up, either the previous frame isn't recorded or there is a bug. If it's a bug, please report it to this thread. Please include screenshots and any lua errors that may have occured while, before, or after the situation. If you don't have any errors, please explain what you were doing that may have caused the bug.
Press the record button again after you're done posing.
Finally, press the play button. If you've followed the steps correctly, and HAT didn't break on you, your animation should play correctly.
If not, well, complain in my facepunch thread about it.
If you did create a successful animation with HAT, why not share it? Share your videos or animations in my facepunch thread.
Remember to have patience when creating animations. Patience is key. Wax on, wax off. If HAT lags for you for any reason, go to the Settings tab and lower down the options. Playing with the settings will really optimize HAT by buttloads.
You can change the way your object moves by changing the tween type. The default tween type is "Linear" which means it moves uniformly in a straight line. Tween types allow the object to slow down or speed up or even both. (wowowowowow)
You can also change how long the frame plays. Maybe you want to make a fast punch, change the frame length on the bottom right corner to a lower number, then press record. Default frame length is 0.5, which is half a second. You can make the frame length anything you want. Setting it to 0 will make the frame transition almost instantaneous (more like 0.01 seconds.) You cannot set it lower than 0.