Polarity refers to the overall electrical charge a molecule possesses. This value (measured as a dipole moment or µ) results from the sum of charges within a molecule’s electron bonds. (e.g. bonds 1+-1=0 a neutral charge; 1+1=2 a positive charge: and -1+-1=-2 a negative charge.
For example, methane (CH4) has a net neutral charge but, methanol (CH3OH) has a net positive charge.
With the addition of an oxygen atom, CH4 forms an OH (hydroxy) group becoming CH3OH - increasing its neutral charge so that it becomes positively charged or polar. (N.B. this is a theoretical reaction, methane cannot be directly converted into methanol, yet).
The compound’s name also changes from methane - with the suffix ‘ane’ representing the single bonds - to methanol with the suffix ‘ol’ representing the addition of the hydroxy (OH) functional group. In chemistry naming, or nomenclature, is very important - as the name of a compound usually indicates the type of structure or the properties it has.