How are bits put on a bus, the i2c for example?
I2C is a form of serial communication (&lt;= read that article).

The data ("bits") are transferred as a sequence.

Usually it is some application software that determines what data needs to be send, what address must be used and what data must be send to it.

Then an I2C controller takes that information and puts it on the I2C bus (the actual wires). The I2C controller consists of transistors which form a certain logic operation which is designed to be have in the way I2C needs.

Before diving into I2C (which can be a bit complex for a beginner), have a look at a simpler protocol called SPI

I say "protocol" and by that I mean something that describes the way I2C (or SPI) works including the voltages on the bus wires.

Then later read more about I2C here.