Check over your license information in https://www.directadmin.com/clients to see which OS the license is set to, and confirm the correct OS is set in the license. This controls which binaries are downloaded, so it's important it's set correctly.
Grab the setup.sh and install DirectAdmin:
chmod 755 setup.sh
and follow the instructions and answer all questions.
While the setup.sh is running, I like to open a 2nd ssh terminal to get the perl cpan modules going, if SpamAssassin is going to be installed. This takes a while, and is unrelated to the main install, so the sooner the better. Basically just step #1 of this guide for now: https://help.directadmin.com/item.php?id=36
This step is not "required", but helps things in parallel. (Note: rspamd is another option, compiles and runs much more quickly than SpamAssassin)
After the setup.sh install is done, the login info should be displayed. If you lose, it a copy of that output can be obtained by typing:
tail -n 21 /var/log/directadmin/install.log
At this point, you should have a vanilla install of DirectAdmin, but there are other steps we recommend. I'll list the main ones here.
Setup CustomBuild to check for new versions weekly, but not update automatically (can be setup however you wish):
./build set cron yes
./build set email email@example.com
More information on this in step #3 of the Basic System Security guide. Note that the CustomBuild 2.0 plugin should also be installed to new DA boxes by default now, so you'll see notices in the Admin Level interface.
There are many other things you can do, but this is a solid starting point.