Here is a selection of reviews that can be useful to learn about microlensing and its applications.
"Microlensing Searches for Exoplanets" by Y. Tsapras (2018)
"Microlensing Surveys for Exoplanets" by B.S. Gaudi (2012)
"Astrophysical applications of gravitational microlensing" by S. Mao (2012)
"Planetary Microlensing: from Prediction to Discovery" by N. Rattenbury (2006)