Microphones- speaker vs mic preamp?

I hope this is ok to ask here. I play electric guitar and am looking into getting a microphone so my vocals can be heard over the guitar, drums etc. I’m new to microphone gear, can I get some thoughts on investing in a mic preamp vs speakers? If it makes a difference, my ultimate goal would be to perform live. Thanks so much!

Edit- looking at the Shure SM58 for the mic itself