how do plants remove CO2 from the atmosphere

In simplified form they take in CO2 and H2O and form sugar and oxygen.

6CO2 + 6H2O ==> C6H12O6 + 6O2(gas)
Plants use CO2 that humans exhale and emit O2 which humans use to breathe.
Plants live and humans live. That's a good reason to keep the forests and plants systems healthy.