Hannes,
If activity steps are assigned to activity, you can control Physical progress using activity steps. By default it is weighted proportionally by the number of steps but you can defined it’s weighting to have accurate production steps progress. You can activate the control by setting Project Window-> Calculation tab-> under Activities-> tick or mark Activity Percent Complete based on activity Steps. When this settings is selected all Physical % Progress is controlled by activity steps if activity steps is assigned to activities. If no activity step assigned then Physical % Complete still need to update manually.

Kumar,
An activity’s primary resource is typically the resource who is responsible for coordinating an activity’s work. The primary resource updates the activity’s start date, finish date, and expected end date. In addition, if an activity has any material resources, the primary resource may be responsible for reporting the material resource’s hours/units. If you don’t want resource to control your activities untick Primary resource box.

Primary resources are also responsible for editing the physical percent complete when weighted steps are linked to activity percent complete for the corresponding activities in a selected project.