Ceacht 2:
tá	is	v	
níl	is not	[contraction of (ní+bh+fuil}]
neg. dep. form of 'tá'	
an	the 	def art	
lá	day	n m5	
oíche	night	n f4	
aimsir	weather	n f2	
maidin	morning	n f2	
go breá 	fine	adj.	
go deas	nice	adj.	
go maith	good/well	adj.	
go dona	bad	adj.	
go hálainn	beautiful	adj. #prefix#	
go hiontach	wonderful	adj. #prefix#	
tá sé	it is 	[v] + [pron]	
níl sé	it is not	[neg. dep. form of 'tá'] + [pron] 	
anois	now	adv of time	
today	inniu	adv of time	

níl: Is used to make a statement NEGATIVE.

There is no INDEFINITE article in Irish.
To say "a day",just use the NOUN on its own:'lá'.But, 'the day'='an lá'.

Notice the noun "maidin" (morning). When it is used with "an" it becomes an mhaidin. This addition of the letter "h" is called LENITION.
Singular feminine nouns in the Common case ( subject or direct object) require lenition when possible.

The list of adjectives on page 8 are used with the PARTICLE "go" which is required when these are used in the manner described.

In this lesson, adjectives are used as 'predicative adjectives' as in "Tá an aimsir go breá". In English it would be "The weather is fine". The adjective follows the verb in English 

This lesson shows us how to extend our basic sentence structure a little by adding an ADVERB to the end of the sentence:
[verb] + [subject] + [adjective] + [adverb]

Let us now use this new construct to analyse some of the sentences:

[Níl]+[an lá]+[go maith]	-The day is not good ( {-} statement, no adverb)
[Tá]+[an aimsir]+[go dona]	-The weather is bad ( {+} statement, no adverb)

[Níl]+[sé]+[go dona]+[inniu]	-It is not bad today ( {-} statement)
[Tá]+[sé]+[go hálainn]+[anois]	-It is beautiful now ( {+} statement)

Footnote:
{+} = Positive
{-} = Negative