Security authorizations assignment

Hi,

I'm new to security.

I want to know the procedure to provide authorization to a single user for a particular transaction code. I know the SU53 or the ST01 trace and how to find the objects being checked. But what I want to know is how you actually add them to the user profile. I do not want other users to get access to the transaction (for eg when I assign it to a role, other users having that role will also get the accesss?)

I have tried looking at resources, reading notes etc. but haven't found a step-by-step explanation of this.

Please help.

Thanks