The saturation vapor pressure curve in the figure above shows the relationship between parcel temperature $T$ and the saturation, or equilibrium, vapor pressure $e_s$. Most parcels have a temperature $T$ and vapor pressure $e$ that result in the parcel being "unsaturated." That is, the parcel's vapor pressure is lower than the pressure needed for the rate of condensation $R_c$ to match the rate of evaporation $R_e$ ($e < e_s \Rightarrow R_c < R_e $). In this case, we cannot "see" the moisture in the parcel - the parcel is not part of any dew or cloud formation.
The temperature for which the parcel's vapor pressure $e$ would be equal to the equilibrium vapor pressure $e_s$ is known as the dew point temperature $T_d$. The dotted lines on the figure show the direct connection between $e$ and dew point temperature $T_d$ for an air parcel, as well as the direct connection between parcel temperature $T$ and equilibrium vapor pressure $e_s$.
For dew or cloud formation, the vapor pressure $e$ of the parcel must be equal to its saturation vapor pressure $e_s$. (Actually, fog and cloud formation will begin for vapor pressure slightly less than $e_s.$) If the vapor pressure of a parcel is well below the requisite equilibrium vapor pressure, the temperature of the parcel must decrease to its dew point temperature $T_d$, the vapor pressure of the parcel must increase to $e_s$ by the addition of more vapor, or some combination of temperature decrease and vapor pressure increase must occur so that the vapor pressure is "close" to the equilibrium value.