In every case of an offence punishable with imprisonment as well as fine, in which the offender is sentenced to a fine, whether with or without imprisonment, and in every case of an offence punishable [with imprisonment or fine, or] with fine only, in which the offender is sentenced to a fine.]it shall be competent to the Court which sentences such offender to direct by the sentence that, in default of payment of the fine, the offender shall suffer imprisonment for a certain term, which imprisonment shall be in excess of any other imprisonment to which he may have been sentenced or to which he may be liable under a commutation of a sentence.
First para explains that by committing any offence if the offender is awarded with imprisonment and fine then the offender can be only fined whether with or without imprisonment. In this paragraph the imprisonment is replaced with fine.
In second paragraph if the offender is awarded with imprisonment and fine or with fine only then if there is default in payment of fine, then as per the decision of the competent court, offender is liable to undergo an additional term of imprisonment. Court is only empowered to provide with additional imprisonment in certain cases.