Save and exit are pretty obvious for the most part.

Exit closes the program. If you have any pending changes you will be given an opportunity to save them.

Save is a little slippery though. It comes and goes at various times. Usually to avoid confusion in some of the windows for performing things that are not directly related to the neighborhood characters. Things like CMX Building and Importing Textures. At other times it will show up but be grey or disabled. Basically this means the screen you are in effects the character but that there currently are no pending changes. If it is enabled then that means there are pending changes from a change either by you or the program. An example of a change by the program is opening a screen where the assigned skin was not found. If so SimEnhancer 3D will randomly assign a new skin. That can help fix missing skins as well. Anyway, SimEnhancer 3D stores any pending changes until you do one of the following.

If you do not like a change you made you can click the drop down list for the neighborhood and reload the neighborhood choosing to cancel any pending changes. Keep in mind that when doing so any and all changes made since the last save will be dismissed.