Mask vs salt

Hi!

I'm new to hashcat and just trying it out so please take it easy on me. I read about the mask attack and I know about salting.
If I have one fixed salt and a mask with some static characters, are they different?
Let's take for example:
1. 10 = md5($pass.$salt) + mask ?l?l?l?l + [hash]:SALT
2. 0 = MD5 + mask ?l?l?l?lSALT + [hash]

Is there any difference between the above two run modes? If so, what are the differences?

Also, I can't find the difference between the straight mode and brute-force. Can someone explain the differences?

Thanks a lot!