what is the difference between versteht and verstehen?
Same verb, just different forms. 'Regular' verbs in English have only two forms: the name of the verb (understand) and a second form adding an 's' at the end. So, "I, you, we, they" understand and "he, she, it" understands. German, however, has more endings for 'regular' verbs.
The website below provides a good review:
I am not an expert in Deutsch but I know this verb usage. It is used as below for different personal pronouns. Ich Verstehe - I understand Du Verstehst - You understands Er Versteht - He understands Ihr Versteht - You (plural) understands Sie/Wir Verstehen - They/we understand. Sorry if there is any mistake, I just started learning Deutsch.