You have a favorite bar on top of the list, can see if you generals are charged and get their current level, attack...
On top right you'll find the current used general, just click on its image and the complete generals list shows. You can click on the image once more to close the list.
On the generals list you can hover over the images and see their current attack, defence, level and the info. Just click on the general you like to set, the list closes and the general will be loaded.
The star will become a plus sign when you hover over it. Click and the general will be shown in favourites bar on top of the other generals.
When the general already is a favourite, click the star will remove it from there and move it back into the list.
If fully charged, the bar will become green.