Hi Murthy,
The methods of creating a mechanism joint is a combination of static constraints. When an assembling a component with static constraints you typically need to define three constraints to make it full constrained. However if you only applied two, you can convert that to a mechanism constraint.
For example, when you assembly with a insert constraint and a mate constraint, you can convert that to a pin joint (mechanism constraint). A pin joint is defined by axis of alignment (insert) and translation plane (mate). You do not have to delete and create over again. In the dashboard for the assembly, there is an icon to convert from static to mechanism or vice versa.
I have accepted you into the PTC U training at
http://first.ptculms.com.
Take a look at the mechanism course.
Thanks,
Mark