Could you please provide me instructions on how to add more data store space to my exisitng 1 TB HDD, since I have place 2 more ,1 TB HDD in the server slots.
What would I have to do next. any documentation is good .
The safest way is going to be to create a RAID volume with all the disks in question. If you only started with one disk, this may not be a possibility. In that case, you'll need to migrate those VMs off to some other storage and reconfigure the available disks to be RAID members. Exact steps depend on the hardware vendor of your RAID controller and are beyond the scope of this forum.
is there a kb on how to add a temporary datastore to move my VM files so that I may attempt to configure all the disk including the current active one in a raid configuration and then move the VM back with the minimal effort ?
No, because it's just like adding any other datastore. You've got to have a device to present for ESXi to consume that does include any of the RAID candidates. If you have that, it's just another datastore followed by svMotions.
If you have only one datastore at the moment I would highly recommend to create another new datastore rather than expanding an existing one.
Having one datastore only is not a good idea.