How To Access My PostgreSQL Server From Another PC Securely?
How to connect should be trivial: fill the appropriate values into the pgAdmin dialog (host, port, user, database). If I remember correctly, pgAdmin calls the database "administrative database" or similar.

This is fairly secure, if you want to do better, here are some ideas:


Use the scram-sha-256 authentication method rather than md5. This requires that you change password_encryption to scram-sha-256 on the server and assign a new password to the user.
Limit the pg_hba.conf entry so that only one user can connect to one database from a single host, for example

host databasename username 12.34.56.78/32 scram-sha-256

For better security, don't allow remote connections as a superuser.
For transport security, you can enable SSL connections. Without that, the communication between database client and database server is unencrypted.