Question

how to know this sentence is simple present tense​

Answer 1

Explanation:

if there is singular subject and first form of verb with s/es in a sentence then the sentence is simple present tense

if there is plural subject and first form of verb without s/es in a sentence then the sentence is simple present tense

Answer 2

It is very simple though. If you want to determine whether the given sentence is in simple present tense then for the first step you need to check its Tense.

A sentence being in simple present tense will have a present tense like : Do, Does, Sing, Sings, Dance, Dances, etc.

On the other hand if you look at simple past or simple future, you'll notice that

Past sentence has Past participle like

Sang, Dance, Ran, Etc.

And Future sentences have will/shall used to hint the reader that the Sentence is signaling towards possible future actions.