The './configure' command is used when you're compiling software from source. Since you don't seem to know it may I advice you to take the easier way? When you want to install software on Linux the first try should always be to use the package manager which will take care of almost everything including dependency resolving. If you don't have the software you want/need available in the repositories for your distro, then search Google to see if someones has gone to the trouble to create one. Always be careful with software from unknown sources! In a last resort, when all else fails, that's when you turn to source code, install dependencies, compile and install the software you want.
In relation to the software you want, Apache Cassandra, you have another option in between. They offer a binary package also which frees you from the need to compile. You can download it here
. The one with the word bin in its name is the one you want, not the one with src which holds the source code and will need to be compiled.
I even found a how to guide, easy to follow, just change the path where you unpack the tar.gz to suit your needs and you're good to go. Have a look at it here
Hope it helps.