What type of verbs are sang, felt and went?
The given forms are example of Past Simple forms of irregular verbs.
The regular verbs create their Past Simple and Past Participle forms by adding "-ed" suffix. Examples: play - played - played, cry - cried - cried, and others.
Irregular verbs do not form Past Simple or Past Participle using "-ed" suffix. They can have:
all 3 forms different: see - saw - seen; sing - sang - sung; go - went - gone etc.
Past Simple and Past Participle equal but different from infinitive: bring - brought - brought; stand - stood - stood; sit - sat - sat; etc.
all 3 forms the same: cost - cost - cost; hurt - hurt - hurt; cut - cut - cut etc.