... Like the 74LS245? What is the purpose of this IC?

It is a buffer between two other circuits, but is capable of bidirectional flow of data. It also has an enable pin which allows three-stating one side of the buffer, so that you can drive the bus only when required (useful for interfacing logic which lacks its own three-state logic).

I see, so an IC like the 6522, or a standard ASRAM would be 3 state as well, because of the Enable pin? The enable is the 3rd state?

Yes, although some devices can be more complex since there are, in essence, multiple enables. The 6522 has several chip select inputs, and the ASRAM chips will typically have one chip select, but also a "OE" (Output Enable) pin as well. To read data from an ASRAM chip, for example, not only does the chip select need to be asserted, but also its OE pin too.

So what would be the purpose of having more than one CS pin then. Like the 6522 with CS1 and CS2?

(sorry for these lame questions... I'm self teaching... )

The two device selects are to help ease device decoding. For instance, you can connect CS1 to A4 and /CS2 to your decoding logic. You could then connect /A4 (inverted A4) to the CS1 of a second chip with its /CS2 connected to the same line as the /CS2 of the first chip.

If you want to decode each chip using just one select, then you can just wire the other device selects to their active states and forget about them. This is how I selected my 65C22's on my SBC's.

Daryl