I have a 30 gallon hot water tank installed at present I want to and a 40 gallon tank to up the total gallons of water for use. I plan to hook the in parallel. Both tanks are electric

You didn't really ask a question so we will make some assumptions here. Do you have adequate electrical supply for the heaters? Each one should be on a 12 or 10 AWG and appropriate 240 VAC breaker depending on the wattage of the elements which can run from 3,500 to 5,500. As far as plumbing, the output of one goes into the cold water input of the other. 2 TPV valves are needed. I would also have a separate gate or ball valve to each heater so they can be shut off separately in case you need to disconnect one or the other.

Personally I think you should buy one big one... it might cost more up front but its going to save you in electric in the long run... as well as space and time to install... because eventually BOTH are going to need replaced at some point.