Before you install LimeSurvey, you should check the manual[1], in
particular the sections for a new install[2] or for updating[3] an
existing installation.

 [1] - https://manual.limesurvey.org/
 [2] - https://manual.limesurvey.org/Installation
 [3] - https://manual.limesurvey.org/Upgrading_from_a_previous_version

You will need to provide a database for your LimeSurvey installation.

This assumes you have some knowledge of your preferred DB, and
already have it installed and configured. If not, please refer to a
relevant Gentoo DB guide.

Once you have a database ready all you need to do is to go to this 
location

http://${VHOST_HOSTNAME}/${VHOST_APPDIR}/admin/

and provide the credentials required for the database access.

If you installed into a vhost, for the above address to be accurate,
you need to pass -h "<host>" and -d "<install dir>" into webapp_config.
The protocol is hardcoded, so you'll have to use https:// if you're
using an SSL / TLS connection.

The default limesurvey user and password for a new install are:

username: admin
password: password