The older Search feature was moved into Windows Explorer itself, you can find the search bar in the upper right- it is a textbox with a magnifying glass on the right side. You effectively use My Computer or another mechanism so you are looking at the folder you want to search, and then you can type what you are looking for there.
If you are open to alternatives, an excellent File Search tool is called "Everything" by Voidtools. it can be found for download
here. It provides a much more straightforward interface that will likely be more familiar to the older "Find Files" tool in XP and earlier; and it is blazingly fast- I can find some file I remember having somewhere on all of my 3 hard drives within a few seconds. The only limitation is that it can only search based on the filename, so if you are searching for that document where you remember using a certain phrase in it won't be very helpful.