And if you get one account banned, can you use other created earlier, or buy new one
or this can be considered as ban evasion?
It's not just your account that gets banned, you as a person are banned from using the forum.
If you create another account or continue to visit from your already active alts, aswell as if you buy an account,
that indeed is considered ban evasion, and usually results in a longer ban for both, your main account and the account you used to evade the ban.