Yes, it is dual-direction. It may both drive the bus, and listen on the bus.

I took a quick peek at a datasheet from TI:
http://focus.ti.com/lit/ds/symlink/sn75176a.pdf

The little chip has 8 pins.

Pin 3 - DE - is described as Enable for outgoing data. In the datasheet linked above there is a logic table showing the function of this enable signal together with the D data signal.

The logic table shows how data in on D (when enabled) will affect the differential outputs A and B.

One more logic table shows how data received on A and B (together with the enable signal /RE) will affect data from the bus to the signal R which is data to your microcontroller.

So, these two logic tables shows quite much of how you connect the chip. The schematic symbol should also help explaining how to connect the chip.

Figure 15 shows how you build the network using the chips.

So my question is still: What is it you are missing in the datasheet? You have data signals D and R to connect to an UART on your processor. And you have enable signals DE and /RE to connect to one or two output pins on your processor. Two pins if you want to be able to listen to your own transmissions. One pin if you want to mute your own transmissions.