Anyone good with SPF records? Help needed.

Wanting to setup an spf record for my server, never done it before.
Could someone explain it to me?
v=spf1 a ip4:x.x.x.x mx ~all
x.x.x.x is my mailserver address but do i need to use x.x.x.x/24 and not just the exact IP or will the above code just work fine.
The reason i am making this spf record is that recently i have been bombarded with bounce back spam emails from several mailer daemons containing email i hadn’t even sent, so obviously spammer email spoofing my address.
Thanks.
Answer #1
This is how all my SPF’s are setup:
v=spf1 ip4:x.x.x.x +a +mx + ?all
Note, you can list as many IP’s as you need. The only reason to use CIDR notation (/xx), is to list an entire IP block.