"Tha sinn a' ceannach IRN BRU."

Translation: We are buying IRN BRU.

[eggfulaura]

Why is there a (') between (a) and (ceannach)?

[jan_Awikiwa]

you may have noticed that with other verb, you have ag (e.g. ag iarraidh).
ag is the full form, but when the verb begins with a consonant, the g gets dropped, leaving a'.

In English, a similar thing happened with the word an/a. the original is an (an apple) but when the next word begins with a consonant, we drop the n leaving just the a (an person -> a person), but we don't put in a apostrophe for some reason.