Let's look at how to deal with materials! Look under Tables in the menu, and pick the appropriate material table. Here is a laser material table for example.
You can add materials, by clicking on the + Empty row Button.
If you've ever used excel, this should be quite familiar. Click on the cell and you can change its value. If you want to move fast, after you've entered the value, you can use the tab key followed by enter.
You can change the row-names to something more descriptive than the auto-generated ID if you want, by clicking the pen icon right next to it, and then the checkbox to confirm.
While you can change the row names - do not change any of the column names (unless you have a reason) - as these are referenced in the calculation pipeline.
You can remove materials by clicking the pen icon right next to the row name, and then the trashcan.
Remember to save!
Always remember to save your table after you've made updates to it.