The person who first registers the account is viewed as the Super Admin. It will be up to them to invite other personnel to join the account (2-3 minute process).
For example, the Professional Plan (which all free trial users get access to) allows the Super Admin to invite other personnel to take on the roles of Administrator (someone who can help with operating the account) and Planner/Broker (whose clients will be surveyed).
There's no limit on the number of personnel allowed to join an account. However Administrators and Planners/Brokers have restrictions on what functions they can access.