The flow of electricity flows from positive to negative channels channels. With a direct current of electricity if we hold only the positive cable (but not holding the negative cable), power will not flow into our bodies (we are not exposed to strum Tuesday). Similarly if we just hold a negative line.
With electricity alternating current, electricity can also flow into the Earth (or the floor). This is caused by an electricity system using the Earth as a reference voltage neutral (ground). This reference, which is usually in pairs in two places (one on the ground in an electric pole and another one on the ground at home). Therefore, if we hold the power source and our feet are treading the Earth or our hands touching the wall, the voltage difference between the electrical cable in hand with tension in the legs (ground), making the electricity flowing from hand to foot so we will experience electric shocks ("exposed strum Tuesday").
Electrical power can be stored, for example on a battery or batteries. Small, for example electricity stored in batteries, won't stun effect on the body. The car battery is great, there is usually a slight stun effect, although not too large and dangerous. Electricity flows from the positive pole of the battery/batteries into the negative pole.
