How to merge cylinder face with torus? (I apologize if this is a dumb question, I am a graphic designer who is new to the program.)
Hi! I'm currently working on a menstrual cup render and need to add a pull ring to the bottom of the cup. IE I need to merge/join this face: 
with the top of this ring:

In other places I've seen this sort of ring created through face extrusion, but the cylindrical face in question doesn't have those inset faces. Merging seems to be the obvious solution, but the number of faces and the angles create an issue. What would be the best way to go about this?
As @moonboots has commented, it depends on what sort of transition you want..
If you were using a sub-d modelling approach, you would keep your pre-subdivision topology to a minimum:

By having only 8 vertices in the circumference of the cup, you make picking a hole with a matching number of vertices from the torus relatively simple:

Allowing you to use Bridge Edge Loops to make your basic fillet. There's a certain amount of adjustment you can make in the tool itself.
After the bridge is made, you can tweak with tools such as:

The shipped add-on Loop Tools &gt; Circle for the profiles, not forgetting it has an 'Influence' setting, allowing you to interpolate between rectangular and circular
CtrlB bevelling edge-loops, to tighten corners, create creases..
Vertex Menu &gt; Smooth, use with care..
With 'Normal' as you Transform Orientation, and 'Individual Origins'as your Pivot Point, you can make tiny adjustments to individual vertices along their normals.

This shows a basic smooth join, after subdivision, (and a Bevel modifier by angle to sharpen the ridges in the cup):

By having the topology straight and simple, it's relatively easy to make variations, using, for example. simple extrusions of faces along their normals.