Installation

There is a paying SaaS option, in which case your Odoo instance is hosted by Odoo and available at https://ainulindale.odoo.com/ for instance.

Databases

You can export and duplicate databases directly from the web interface (Top Right Menu -> My Databases).

It seems the Payroll module does not have built-in rules for countries. For instance, you must enter manually the rules that will compute your social contributions.
Rules should be either of category "Company contribution" (if the employer pays this contribution) or "Deduction" (if it's paid by the employee, out of the gross salary).
You must first create a work contract for an employee.
To create the entries in the accounting journals, you should click on the "Create Draft Entry" button on the Payslip.

2720 holds the debt of the company to the social insurance institutions.
2850 (Private share account) is used to hold debts of the company to the shareholder.
5700, 5710, 5720, 5730, 5740 are used for various social benefits (health insurance, unemployment insurance, maternity insurance etc).