You can play the first season for free, to extend your game you will need a premium account. Premium account allows you to play unlimited number of seasons with your team, also premium users have access to further game data (like more specific player statistics, player history, etc).
Premium account cost varies depending on the option chosen and length of the subscription:
subscription type
access to game modes
cost
Premium
all game modes
from 1,50 € / month
to 12,00 € / year
Premium Multi
all game modes
up to 5 games can be played at the same time on single account
from 3,00 € / month
to 20,00 € / year
Premium account does not change the basic game rules, so your players won't gain extra skills or abilities, the economy will be the same, your staff skills will be the same, all you will get is unlimited game length, which will show the depth of the game when you will have to plan your transfer policy according to changes in the squad due to retirements, transfers and other events.