I cant understand MR.SINGH loves singing while he is bathing.

This is a gerund or a verb

When we use a verb in -ing form as a noun, then it is usually a gerund. Therefore the first part of sentence uses 'singing' as a gerund.

When we use a verb in -ing form as a verb or an adjective, it is usually a present participle.

In 'while he is bathing', bathing is used as a verb.