nothing works!
Really? Your case would be helped by you telling us what you have actually downloaded, what you have actually typed, what actually happened, and what about it indicates it did not work. At the moment we can guess you are on a Linux box and have no other useful information.
tell me the code above, replacing the parts that should be replaced.
Give me a pony.
cd <path>/qt-everywhere-opensource-src-<version>
"<path>" is wherever you have unpacked the distributed Qt source archive file on your machine. You need to unpack the downloaded file first; it will not happen magically. For reasons I hope are obvious we cannot tell you where you have unpacked files on your machine. "<version>" is the plainly obvious version number that appears at the end of the actual directory name of the unpacked Qt source archive.
Guessing that you have not unpacked the TAR file you mention:
cd
tar xvf {your downloads folder}/qt-everywhere-opensource-src-5.0.2.tar
cd qt-everywhere-opensource-src-5.0.2
./configure -prefix $PWD/qtbase -opensource -nomake tests
"$PWD" is an environment variable. You type it exactly as presented above.
make -j 4
Build the library. You type this exactly as above. Incidentally, these are instructions for building the Qt libraries, not Qt Creator
Your level of understanding suggests to me that you should probably start with the pre-built library or Qt Creator binaries (http://qt-project.org/downloads).