Total Newbie need help

I watched Dr. Vax’s first three tutorials about Freecad. I am using 18.4. I am trying to create a part for my 3D printer. It is a support for my hot end and heat sink. The original support cracked when my nozzle clogged and I had to remove it for cleaning. The printer is an older TronXY and it functions perfectly. I tried, (unsuccessfully), to buy a new carriage online both through Ebay and Amazon but each carriage did not align with the support holes. Since the original part was plastic I thought I would try to create one. The part is 60mm long, 40mm wide eith a centered 8mm x 20mm extrusion at the top (like a tab), IT is 5mm thick. I created the 40x60 body. Put the hole in the center to support the heat sink. Then I created the 8mm x 20mm tab but I do not know how to attach it to the 40 x 60 body to create one solid piece. Any help will be appreciated but please take me step by step as I am totally new to this and don’t know all of the tools and procedures necessary to create the part.

I would create the tab & main body as 1 sketch, then pad it.