If you have a ticket for FIFA 2018 World Cup in Russia you do not need a Russian visa, but only if you are entering and leaving Russia between the 4th of June and 25th of July
. If you're traveling to Russia outside of these dates or if you don't have the tickets, then you would still need to apply for a Russian visa
to travel to Russia. You would also need a Russian visa if you want to stay in Russia before or after these dates (e.g. to go for a travel after, etc)
A ticket for the World Cup alone is not sufficient to enter the country. You need to have
1) a so-called Fan ID.
It's an obligatory document that you would need to enter / leave the country and also to access all the games you have the tickets for. You can obtain Fan ID on the official FIFA 2018 Fan ID website
. One other cool thing about the FIFA World Cup Fan ID is that you can use it to take free trains between the cities hosting the championships and use the public transport for free.
2) the tickets for the games you're planning to visit (or a print-out confirmation from FIFA that your tickets have been allocated)
3) a passport valid at least 6 months after the end of intended visa-free stay (i.e passport should expire 25th January 2019 or later).
If you do travel to Russia with a standard visa between the 25th of May and 25th of July 2018, you would need to register your visa within 24 hours (normally this period is 7 business days, but it was shotened for the duration of FIFA games). Any hotel you're staying in will do this for you for free, otherwise you can ask the company that provided your visa support to do that for you or your AirBnB apartment host (please, confirm with them beforehand if they can do it for you).