The present perfect tense

Na minha humilde opinião é um dos tempos verbais em inglês mais complicados de entender, mesmo porque nós não temos em nossa lingua um tempo verbal equivalente.
Ele é utilizado para se referir a uma ação que aconteceu no passado e tem consequências no presente. Pode ser traduzido tanto no passado como no presente.
O grande diferencial entre escrever nesse tempo ou no passado são as datas.
O past simple é datado e o present perfect não é. Tanto que nós podemos usar o present perfect para se referir algo no presente.
Assim, olhe!

"I've studied English."- Eu estudo inglês; tipo eu já estudo faz tempo e continuo estudando.

Tem mais, quando aparecem os advérbios: for (with a period of time), since (with an exact point in time), ever, never, yet, already, this week (month, year), normalmente teremos o Present Perfect.

I´ve never been in UK.
Have you finished your report yet?

Para entender um pouco mais sobre esse tempo vá a estes dois link:
1. Formação e estrutura
2. Exercícios


Essa tabelinha de verbos irregulares ajuda pra caramba. Num é que você tem que decorá-la, mas tem alguns verbos que a gente usa com mais frequência e é bom guardá-los na memória, certo?
Ah, para formar o Present Perfect verbo to have (has, have) + particípio passado do verbo principal regulares -ed irregulares vide 3ª coluna da tabela.

	Past	Past
Infinitive	Simple	participle

be	was/were	been
beat	beat	beaten
become	became	become
begin	began	begun
bend	bent	bent
bet	bet	bet
bite	bit	bitten
blow	blew	blown
break	broke	broken
bring	brought	brought
build	built	built
burst	burst	burst
buy	bought	bought
catch	caught	caught
choose	chose	chosen
come	came	come
cost	cost	cost
cut	cut	cut
deal	dealt	dealt
dig	dug	dug
do	did	done
draw	drew	drawn
drink	drank	drunk
eat	ate	eaten
fall	fell	fallen
feed	fed	fed
feel	felt	felt
fight	fought	fought
find	found	found
fly	flew	flown
forbid	forbade	forbidden
forget	forgot	forgotten
freeze	froze	frozen
get	got	got
give	gave	given
go	went	gone
grow	grew	grown
hang	hung	hung
have	had	had
hear	heard	heard
hide	hid	hidden
hit	hit	hit
hold	held	held
hurt	hurt	hurt
keep	kept	kept
know	knew	known
lay	laid	laid
lead	led	led
leave	left	left
lend	lent	lent
let	let	let
lie	lay	lain
light	lit	lit
lose	lost	lost
make	made	made
mean	meant	meant
meet	met	met
pay	paid	paid
put	put	put
read	read	read
ride	rode	ridden
ring	rang	rung
rise	rose	risen
run	ran	run
say	said	said
see	saw	seen
seek	sought	sought
sell	sold	sold
send	sent	sent
set	set	set
sew	sewed	sewn/sewed
shake	shook	shaken
shine	shone	shone
shoot	shot	shot
show	showed	shown
shrink	shrank	shrunk
shut	shut	shut
sing	sang	sung
sink	sank	sunk
sit	sat	sat
sleep	slept	slept
speak	spoke	spoken
spend	spent	spent
split	split	split
spread	spread	spread
spring	sprang	sprung
stand	stood	stood
steal	stole	stolen
stick	stuck	stuck
sting	stung	stung
stink	stank	stunk
strike	struck	struck
swear	swore	sworn
sweep	swept	swept
swim	swam	swum
swing	swung	swung
take	took	taken
teach	taught	taught
tear	tore	torn
tell	told	told
think	thought	thought
throw	threw	thrown
understand	understood	understood
wake	woke	woken
wear	wore	worn
win	won	won
write	wrote	written