Range of RF module (and antennae) given then "sensitivity" in dBm?
First of all, dBm is a unit of power. 0dBm = 1mW, 20dBm = 100mW, -20dBm = 0.01mW.

Sensitivity of a receiver is the minimal power of the signal that the receiver still can receive (with the specified error rate). Antenna gain is how much power the antenna can collect, or rather, how much it is better than an ideal isotropic (radiating/accepting in all directions equally) antenna. The units are dBi. Isotropic antenna is 0dBi. Any antenna that has gain above 0dBi usually receives from some directions better than others (for example, there usually is no point receiving from straight up or down). Antenna gain s applicable for both, the transmitter and the receiver.

You also need to know the power of the transmitter (convert it to dBm if it is in mW) and the frequency.

The power received is calculated like this

Pr = Pt + Gt - L + Gr

Where Pt is the transmitter power (dBm), Gt and Gr is the gain of transmitter and receiver antennas, Pr is the received power and L is loss.

If Pr is higher than the receiver sensitivity then your link will work.

Loss is calculated like this:

L = Lfs + Lc + Lo

Lc is the signal loss in cables, connectors etc.
Lfs is the free space loss and Lo are other losses.

Lfs = 32.4 + 20 log(f) + 20 log(d)

Where "log" is the base 10 logarithm, f is frequency in MHz and d is distance in km.

Calculating signal loss is very complex, however, if you assume that the antennas are high above ground and in line of sight of each other, calculating free space loss is enough. In a city or indoors you also need to calculate Lo - this can get very complicated. There are various signal propagation models suitable for different areas and there also is software that can help you calculate it. Those models usually calculate Lo - what you need to add to the free space path loss to compensate for the fact that the signal is not going trough free space.

Another important thing is that the receiver sensitivity is an ideal measure, that is, it only applies if there is no noise. if there is noise, then your signal will have to be stronger.