"You were there yesterday."

[Nick384536]

Sometimes you can use byls, other times not? I don't understand this. Also, is it common to use 'byls'?

[VladaFu]

In speech very common. It is accepted here. If some answer wasn't accepted, you have to tell us the exact answer.

[DOette]

I wrote "Ty tam bylas včera" and it was not accepted. Not sure when to add a "s" and omit "jsi" or omit "s" and use "jsi" or if both are acceptable.

[VladaFu]

The s is an enclitic and follows the second position rule. "Tys tam byla včera." is possible.