Ceacht 11
cé?	who	Interr. particle	
cé atá?	who is?	[interr. particle] + [rel. particle (merged with) v ‘tá’]	
le	with	Prep.	
le Bríd	with Breda	[prep.]+[n]	
ag caoineadh	crying	“ag” + [vn]	
isteach leat	in with you	[adv.]+[prep. pron]	
mar sin	so, therefore	prep phrase	

atá:  The word atá is actually made up of two parts - a + tá.  We have already met the verb tá (is / are) but in this lesson we see it in a combined form with the verbal particle a.  This verbal particle is required following the interrogative particle "cé?" (who?).  It is usually written separately but with the present tense verb tá it is combined to form atá. 
As regards "Cé atá?": The "relative particle" between the interrogative particle "Cé" and the verb "tá" is rarely heard in speech, however it is considered better to include it when writing Irish

In English, we have verb forms which describe activity currently "in progress". These are called "present participles". You may like to think of them as the "-ing" verb forms, e.g."crying" (ag caoineadh).  Irish forms its '-ing' verb forms by putting the preposition "ag" in front of what is called a "verbal noun".