Specialk12, do you want to gain mass or become stronger?
If its stronger you are right to lift weights of which you cannot physically make 1 more rep after the 5th or 6th rep. For this you definately need someone to spot you, so they can take the weight off you when your finished. Cos when under stress of lifting when ur tired if ur on ur own you find u panic and cant get the weight off you, and this can lead to serious injury, a hole thru the floor, or even ur death.
If gaining mass, a weight u need is were you can do 6 to 10 reps until failure (asin till you cant lift it again)
Either way you will need a spotter, the only type of weight training you dont really need a spotter for is toning. Cos when toning the weight you lift isnt that heavy.