You are correct that those levers are designed to be opened with your bare hands. Unfortunately it's usually easier to push the lever closed than to pull it open, so it's easy to over-tighten it.
- Start with the lever open, and facing back as shown in the picture
- Wind the nut on the other side back 2 or 3 turns.
- Close the lever. It should be very easy, and the wheel is not properly attached.
- Wind the nut in until it is tight (finger tight, do not use tools!)
- Open the lever.
- Wind the nut in half a turn.
- Close the lever. It should be firm, but not impossible.
- If it's too hard to close, back the nut off a small amount and try again.
- It it's too loose, tighten the nut up a small amount and try again.
Unless you're unusually weak, not being able to open it means it is on too tight. Even if you are somewhat weak, unless you have disk brakes "as tight as you can" should be ok.
Note that if you have disk brakes it is much more important that the quick release be tight. When you use disk brakes the reaction force is pushing the wheel down, out of the fork. It is better to have the QR slightly too tight than slightly too lose with disk brakes.
Also, the QR lever should always point backwards as shown. That makes it less likely to catch on anything and be pulled open (of throw you off the bike).