Why use SELECT FOR UPDATE?

Question

I have question regarding what purpose we are using SELECT FOR UDPATE? What does it do exactly?

I have 2 tables, from that I need to select rows from table

Answer 1

Still, what's the purpose we are using SELECT FOR UPDATE rather than UPDATE? What's the essential rational behind the choice?

Below is my Thoughts- SELECT ... FOR UPDATE should more likely be compared with SELECT rather than UPDATE. The reason is that SELECT does not retain an exclusion lock but SELECT ... FOR UPDATE does.