Official website with information about travelling to Estonia, Covid-19, security situation, etc: https://www.kriis.ee/en?
Starting form the 18.06.2022 COVID certificate is no longer required for travel to Estonia.
FAQ about the security situation: Security situation in Europe: Q&A | Kriis
Please note that as stated officially by Estonian authorities, there is no current military threat to the security of Estonia: the situation on the external border is calm and our security is guaranteed as a member state of NATO.