Searching for packages
If you are looking for some new software for your Pi, whether it's a full application or just library files, use the apt package commands as shown below. You'll need to be logged on as root or prefix each command with sudo.
Use apt-get update to download any package updates and then write the changes to the local package cache. How long it takes depends upon how recently you ran the command previously and also how many new packages there are.
sudo apt-get update
If you know the exact name of the package you wish to install, you can skip this step, otherwise you can search the cache. Try to be fairly specific in your search to reduce the number of packages found. Use the less command to display one page of results at a time.
sudo apt-cache search search-string | less
Use apt-get install to install the package and any of its dependencies.
sudo apt-get install package-name
I have found that there are sometimes many packages that look, from their description, that they might do the job, but you should determine the exact package you need rather than try to obtain it by trial and error.