fresh start is similar to a reset meaning it reinstall it on the same drive again.
It puts windows on fresh, no extra applications like Steam, Itunes, programming apps, etc. Like if you just got PC from a store.
But it only touches C drive. Any other partitions would be ignored.
Now the two ways to get win 10 on new SSD is clone hdd across onto SSD, SSD needs to be same size or bigger than hdd or it won't work, OR you download the Windows 10 media creation tool
and use it to make a win 10 installer on USB, and do a fresh install onto SSD - which is the better idea in general
Fresh install removes all trace of win 7 before it, no multiple windows.old folders. Its a better idea on a new SSD too
If you choose fresh install, here are a few tips
remove old hdd from PC while you install onto ssd or win 10 might use hdd for boot sector and mean if you later remove it, ssd won't boot
follow this guide: http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html
when you reach the screen asking for licence, click "I don't have a key" and win 10 will continue to install and reactivate once finished