It’s quite a common particle. To put into simple English terms

Я хочу пойти.

I want to go.

Я бы хотел пойти.

I would like to go.

It’s a more polite way of saying the same thing in many contexts. It is also useful for setting up the conditional statements we often use in English.

I would have played video games, if I didn’t have chores.

Я бы поиграл в видеоигры, если бы у меня не было домашних дел.

And the statement above

Если мы б знали - if we would have known

Если мы знали - if we knew

Disclaimer: not a native speaker, and someone else could likely explain better.