basically, any transformer, either step up or step down, is made with 2 separate coils of wire, wound around the same metal base. One coil is called the primary, and the other the secondary. The ac voltage source is always connected to the 2 leads of the primary coil only. As the ac signal moves through the coil, the electro magnetic field it produces transfers the current and voltage to the secondary coil. The 2 leads from the secondary winding are the output leads, which have the desired voltage and current, or the desired signal. The 2 coils are never physically electrically connected in any way, the coils are insulated from each other. They are only wound on the same conductive form. This is called inductive coupling.
A step down transformer has more turns on the primary coil and less on the secondary. A step up tranformer has more turns on the secondary and less on the primary. The ratio of turns between primary and secodary determine how many volts are stepped up or down, ie, 100 primary to 10 secondary (100:10) would step down 120 volts to 1.25 volts. If the ratio is listed, the first number is always the primary coil.
Note: The ratio of turns on a -former does not indicate how many turns there actually are in each coil, it is simply the mathematic ratio of the number of turns between the two coils.
Many transformers do not list the turns ratio, only the primary input/secondary output voltages. Small audio and signal-type transformers are rated by impedances, like 1k impedance primary to 8 ohm secondary.
Also, as voltage is stepped down, the available current is stepped up, and as voltage is stepped up, the available current is stepped down. It is an even exchange.
Edit: however, safely supplying the max available current is still limited by thickness of wire, rating the other components, etc.