This is how to find files in Linux assuming you know some little detail about it.
To find "myfile.txt" in the current directory and any subdirectory under the current one.
find -name 'myfile.txt'
To find for any file named "myfile.txt" on the root and all subdirectories from the root.
find / -name 'myfile.txt'
To find for any file beginning with "file" in the current directory and any subdirectory.
find -name 'file*'
To find for any file that is larger then 1000k.
find -name '*' -size +1000k
For complete options and other usage you can always check the man page of find.