Drum dials are good to assure that you have even tension all the way around the head - which is an important part of drum tuning. In addition, there is an instruction sheet which identifies approx. tension for specific sized shells. However, a drum dial costs almost as much as a set of batter heads.
Keep in mind that if it is a new kit, it probably came with cheap heads. If it's a used kit, the heads are probably dead. In either case you need to replace the heads (at least the batter side).
I would suggest that before you buy a drum dial, buy new batter heads. For a 5 piece kit you're looking at $100 (including the kick). Evans and Aquarian make great heads and Remo have been a standard for years. Make sure you get even tension by tightening all the lugs to finger tightness, then useing a "star" pattern tighten each lug a 1/4 turn with a tuning key. When you get the heads "semi-tight" push down to "seat" the head. Then continue to tighten to your preference. When you tap the head near each lug (about 1" from the rim) you should get the same tone.
A drum dial is not a bad tool, but it will never replace learning to get a sound by trusting your ear.
Keep working at it - you'll be glad you did!!