If you’re using one of the last few Windows OS you would just download the related files, unzip them if compressed, right click on the TrueType Font File and click install. If you have more than one user on your computer, choose the “install for all users” instead of “install”. Restart Fusion and it should be on your list.
Some free fonts won’t work in Fusion. I don’t know why, they just won’t open or won’t open correctly. But I’ve found that to be like 1 out of 10.