"You are welcome, Una and Anna."

Translation: 'S e ur beatha, Ùna agus Anna.

[Fiona.amg]

When do you use "'s" as opposed to "tha" or "is" for is/are? I understand between tha and is, basically "tha" is for description, "is" is for identification, but i dont understand "'s"

[silmeth]

’s is just shorter is that is commonly used before vowels, so you’ll rather see ’s e than is e (but both are possible).

It’s similar to how tha changes to th’ before some words, eg. in a th’ orm that is on me.