Get into config mode, then

myswitch(config)#hostname myswitch
myswitch(config)#ip domain-name YourDomainName.com
myswitch(config)#crypto key gernate rsa

you will be prompted with

The name for the keys will be: myswitch.YourDomainName.com
Choose the size of the key modulus in the range of 360 to 2048 for your
General Purpose Keys. Choosing a key modulus greater than 512 may take
a few minutes.

How many bits in the modulus [512]:

fill in 1024 for the answer (2048 would be better)

myswitch(config)#username admin secret 0 MySecretPassword
myswitch(config)#line vty 0 4
myswitch(config-line)#login local
myswitch(config-line)#transport input ssh
myswitch(config-line)#exit
myswitch(config)#ip ssh version 2
myswitch(config)#ip ssh authentication-retries 3
myswitch(config)#ip ssh time-out 120
myswitch(config)#exit
myswitch# wr mem

If it is an older switch, you probably will want to have this handy