When I am assigning labor to my activity, for, say, concrete pouring, I have 5 labors that have exactly the same cost. So do I use 5 separate concrete labor assignments to that activity? So in the resource sheet I go as Concrete Labor CL1, CL2, CL3, CL4, CL5 and so on and assign them separately? Or I just have one CL resource in the resource sheet and assign that CL to the activity but in that case how do I show 5 labors will be working on it?

It's up to you. If you have 5 Concrete laborers who all have the same rate and you don't care to track vacations, create a Concrete Laborer resource and set the max units to 500%.

If you need to say that one of the laborers is on vacation for two weeks, then setting CL1, CL2, etc is likely better.

got it, thanks.

You're welcome ketanco and thank you for the feedback.

ok actually another question just came to my mind about this...

if you assign 500% to represent 5 labor, then doesnt it create an overallocation problem? I mean you wlil have to level resource later this way no? although you have 5 people available working, you are telling ms project as if one worker works at 500% capacity...

One worker cannot work at 500% capacity. If you have 5 of the same resource, enter 500% in the max. units field for that resource. If you exceed 500% assignments, then the resource is overallocated.