I am trying to follow a video :https://www.youtube.com/watch?v=YgN4Q8vuglI&t=94s, when I go to highlight the letter and then highlight the square to remove the difference, nothing happens?  Does anyone have any suggestions?  I am new and trying to learn, but I need step by step, I don't learn if I can't do it.    I greatly appreciate any help I can get in this project.

Hi. 

It's "hard to guess" what went rong as we don't know the exact steps you took. 

Whenever you select an object or perform a path editing action, keep an eye to the bottom indication bar. It will describe any issue that prevents executing a certain step.

My guess is, you had a text object and converted it to a path (Shift+Ctrl+C) and after that you are trying to subtract a rectangle from the resulting object.

The bottom indication tells in such scenario that one of the selected objects is not a path -but a group- thus the Boolean won't work.

It is a bit confusing indeed that converting the text to path doesn't result in one compound path, but a group of individual characters represented as paths. 

(This way additional info can still be preserved of the text  -like font size and style- and helps typesetting for example. It is proposed to use these info in a development to recover text objects based on such paths as of currently if you convert a text to path, you cannot edit it any further as a text. Accidental typos will be permanent.)

That's just a guess though.

If you not convert the text to path, the substraction should work probably as intended. Depends on the circumstances.

Checklist:

1. Make sure both objects selected are on an unlocked layer (if you are using layers)
2. Make sure not to select more than two objects at a time. If you want to substract more rectangles at a time, first add those together (Ctrl++).
3. Make sure neither selected object is a group. Keep an eye to the indication bar as mentioned above. (When drawing more complex images nested groups may exist upon purpose.)
4. Similarly check if any of those objects are clones/result of clipping/masking/pattern fill/neither has a path effect/rendered geometry fits the "core" of the image etc. This case it's probably self explanatory that neither apply so let's see what else to look for. (Probably very unlikely but a rectangle shape can be the result of a two noded path with a wide stroke and a linear segment. That case there wouldn't be any area described for substracting hence won't appear if the Boolean was performed or not.)
5. Ensure that the rectangle you want to substract is above the text object in the z-order. Should look obvious at a glance if both object are filled and not viewed in outlines only rendering mode, but it can also be a source of errors.

These are of the top of my head. 

Can come across many errors, but that's all natural in an experimenting process.

What's seen in the video can be broken down to a few steps if that really helps -assuming one starts from scratch.

1. Create a text object (F8).
2. Draw a rectangle above (F4).
3. Select both objects (If there are only two object on the canvas, Ctrl+A will select all which will work).
4. Perform substraction (Ctrl+-).

Check this topic if those two tools are not drawing anything visible.

Welcome to the forum!

All I can really tell you to do, is go back to the beginning and make sure you follow every single little step that's shown in the video.  I've watched the video, and it is showing everything correctly.

My best guess about what might be going wrong (since I can't sit on your shoulder and watch you working) is that maybe you don't have both the letter and the square selected.  Did you hear him say to hold the Shift key?  You need to hold the Shift key to be able to select more than one thing at a time.

Or else maybe you need to start with something simpler as a beginner?

Here are some tutorials which are organized for different skill levels.  https://forum.inkscapecommunity.com/index.php