Welcome Wendy.
For the feet and what they do - go to
https://www.singer.com/support and put in 301 for the model number and download a manual. The manual will have instructions on how to use the various feet. If you google the numbers you might want to add "singer parts" and usually you will see the name of the foot.
I sincerely doubt that the 301 will fit a 99 cabinet. The 301 cradle was made to fit the cabinets for the 400 series. You might want to read through some of the threads such as
Picture needed of 301 cradle mounting brackets and
Cradle for 301
Janey - Neat people never make the exciting discoveries I do.