Q: How do I mount my flash drive on the disc utility?

My flash drive is not showing up on the desktop (& I've tried more than one so it's not the flash drive). This happened once before, but it was after downloading the most recent update. This time I haven't changed anything & it was working fine 2 days ago. I remember from last time we had to open the disc utility so I did that & I can see it (them) there, but it says unmounted. I can't remember the next step & I don't want to make it worse.