@Cordova Man I've complied many informations on the same topic to be easier to find where to start:
How the start on OpenBOR
ASU is a great tool to cut sprites, but it will cut the sprites into tiny pieces if there is any empty space on it
View attachment 5823
or will group many sprites as one image if there isn't enough space between them (see the blue effect):
View attachment 5820
Another case of not enough empty space around the sprites (the text above it will glue everything togheter, and the last frame will affect it too)
View attachment 5821
This is how it should be:
View attachment 5822
Keep in mind that, after you use this tool, it will crop each image to a different size and this will give you a lot more work when programming, as you will have to provide an axis (offset) for each frame.
It is recommended to use a single image size and align all frames within that image. With this, you can reuse the offset and bbox in other frames of the same character (or others).