Verbs come in different forms and those forms are partly determined by the tense of the verb.
The five forms of verbs are:
The verb sing has the following five forms:
sing, sings, singing, sang, sung
For most regular verbs, two of those forms are the same.
The verb walk has the following forms:
walk, walks, walking, walked (past and past participle).
For some irregular verbs, three of those forms are the same.
The verb cut has the following forms:
cut (base, past, and past participle), cuts, cutting
1. The base and -s forms of the verb are used as part of the present tense, for actions that are happening in the present.
2. The -ing form of the verb is used as part of the present progressive tense to show that something is happening at the moment.
3. The past form of the verb is used as part of the past tense, for actions that happened in the past.
4. The past participle form of the verb is used as part of the past perfect tense to show actions that are continuous or happened over a period of time. It is usually combined with the verb has/have.