How to create a rib ?

There are two tutorials within the library that are helpful in creating ribs.

SolidWorks Advanced 3D Part Modeling Tutorial

also

https://grabcad.com/tutorials/rib-angle-in-solidworks--1

The first link leads to a video showcasing advanced techniques, while the second link breaks down ribs into a few short but necessary screenshots.

Assuming there are four lines in your sketch making a closed profile, you are on the right track, but it won't work.
The Rib tool only works with open profile sketches. So let's assume you are planning to use an extrusion instead.
With an extrusion the profile you've drawn will go in a straight line, so it won't follow along with the curvature of those cylinders.
A better way to make this model is to add the rib before you cut the holes through those cylinders. That way you can make the rib sketch overlap the cylinders with no risk of accidentally filling them in.

Here is an image showing three different ways to make the rib. Which method you use does not matter in this case. The green and orange "ribs" are made with simple extrusions. The purple rib is made with the Rib tool.
Zoom in on the image. The type of sketch drawn does matter. Both of the extruded ribs require a closed profile. The rib requires an open profile. The sketches for each feature are highlighted in blue.

The Rib tool basically operates with the Up To Next end condition, but it does so in three directions at once. If the Rib won't intersect the model in one or more of those 3 directions, the feature will fail.

I don't want to troubleshoot your part(s) based on a text description. If you post the SOLIDWORKS model, we'll be able to easily see what is wrong.