Can i directly add a user under any feature or topic without asking them to email activation?
First, see my reply to your other topic. It might help if you’re confused because of the wording of topic/feature on meta.
Next, you can sort of accomplish this. If you invite a user to a topic (click the invite button at the bottom of a topic) they’ll get an email with a link to account creation which will let them immediately reply to the topic. Technically, they never got an email activation. You do, however, need to give them an account somehow and accounts must have an email address. Email must also be working in order to have a viable Discourse install.