With Gentoo you install software using emerge, e.g. for KWrite you would open a console and type emerge --ask kwrite (using --ask to get an overview of necessary dependencies and USE flag options before confirming). If you are unsure of the name of a package, you can use emerge --search to see all the packages with a word as part of the package name — e.g. emerge --search network will list all available packages with "network" as part of the name.
