Are you Russian? No. Right, then you’ll be needing a visa.
For a Russian visa you will need a letter of invitation before you apply for a visa.
What is an LOI - It's a letter of invitation is issued by a Russian organisation with is registered and accredited with the Ministry of the Interior for the Russian Federation. The letter basically contains information regarding your travel plans within the Russian Federation and vouches for you whilst in the country.
If a person is required to obtain a visa to enter the Russian Federation then a Letter of Invitation is necessary in order to complete the visa application process and must be procured prior to the submission of the application.
To avoid the headache of applying for these yourselves, we recommend The Visa Machine.