here is a basic overview of crafting. https://ffxiv.consolegameswiki.com/wiki/Crafting

when you switch to the crafting class the skills on your hotbars will change to the basic crafting skills. At first you'll only have access to synthesis skills and you can only use these skills while crafting. so after clicking begin, you'll kneel then you need to use basic synthesis to actually make the item. you'll probably need to use the skill 2 or 3 times to finish the craft. when it's done you'll get a message stating the craft has finished.