Although MakeCode lets you test your program on a simulator, you'll want to assemble the Musical Glove beforehand. That way you can make sure the code works the way you think it will when everything's in motion in three-dimensional space.
Peel-and-stick Velcro dots (or similar hook-and-loop connectors) are an easy way to put everything together. Here's what to do:
Stick four Velcro dots on the back of the Circuit Playground Express (CPX). Press firmly.
Take the matching halves of the dots and press them onto the CPX dots, with the fuzzy/scratchy sides together and the glue side facing out.
Put on the glove. Position the CPX on the back of your hand, with the JST socket for the battery holder pointing towards your wrist. Press the board firmly onto the glove so the glue sticks tight to the fabric.
Now gently detach the CPX, making sure the Velcro dots separate, leaving the bottom dots on the glove. Press them again onto the fabric to bond them firmly. Use care whenever you remove the board to avoid accidentally pulling the dots off the fabric.
Insert batteries into the battery holder. Add one or more JST extension cables if you want to slip the battery holder into a pocket or clip it onto your clothing or an armband. Otherwise, you can use Velcro dots as you did with the CPX and attach it directly to the glove.
Plug the cable into the CPX.
You're ready to start coding the CPX and test it out with your glove!