What is: Rib 4, rib to last 4sts...

Hello, I am trying to knit my first sweater and am confused as to what the instructions are asking me to do.

The instructions read
Rib 4, rib to last 4 sts
inc 2 st/s evenly across, rib 4…
51 sts

I currently have 49 stitches and I know that I am meant to add in 2 more to get 51 stitches but that is about the extent of my understanding.

Any help would be greatly appreciated.
Thanks

Welcome!
“Rib” means to work in whatever rib pattern you have been using, knit 2, purl 2 or knit 1, purl 1.
There are often directions similar to these at the transition in a sweater between the ribbing and the main body of the sweater.
Work across in your rib pattern and place the increases after about one-third and two thirds of the sts have been worked. The increases will disrupt a rib but don’t let them affect the overall pattern of ribbing.

What is the name of your pattern?