To have--Entenda esse verbo.

                       O verbo " have".
Verbo, a grosso modo, é o mesmo que ação, acontecimento.
O verbo have é particularmente interessante pois além de ser usado
como verbo principal ele também ajuda na conjugação de outros verbos, de forma correspondente ao nosso português.
I have a bicycle= Eu tenho uma bicicleta.
I have lunch at noom.= Eu tenho almoço meio dia.
Would you like to have a cup of tea?
Gostaria de tomar uma xícara de chá?
ou: Gostaria de beber uma chícara de chá?
Note que no último exemplo eu não traduzo como: Gostaria de ter uma xícara de chá? a tradução não é exata, ela serve para te dar uma idéia da realidade.
O passado de have é had, e o has é usado nas 3ªs pessoas do singular no presente.
O passado particípio expressa algo que está feito, acabado, terminado.
Por exemplo o verbo ir:
Eu vou-presente= I go //( futuro = eu irei.) I will go.
Eu fui-passado = I went
Eu tenho ido- passado particípio= I have gone.
Note que no último exemplo eu não posso dizer Eu ido, o verbo tenho é o meu auxiliar, igualmente em inglês eu
não posso dizer I gone, eu preciso do
verbo auxiliar have, I have gone.

Aqui é onde você forma o present perfect, usando o verbo have como auxiliary e o verbo principal no past participle.

Muitos verbos em inglês tem o past simple igual ao past participle, e o verbo have te mostra que o verbo principal é o participle. Por exemplo:
Eu trabalho= I work
Eu trabalhei= I worked
Eu tenho trabalhado= I have worked.
Note que no português o verbo trabalhar no passado é diferente do verbo trabalhar no passado particípio, ou seja: trabalhei e trabalhado,
mas no inglês eles são iguais, o verbo have é que te mostra quando o worked é simple ou participle.
I worked= past simple.
I have worked= present perfect, worked = past participle.

O verbo auxiliar é que dita o tempo que está sendo usado na conjugação, não o verbo principal.

Note que apesar do verbo worked aqui estar no passado, neste caso o past participle, o verbo auxiliar have está no presente e é ele que dita o tempo aqui.
I have worked= present perfect.
I had worked= past perfect.

Verb have tenses:
Present continuous: I am having
you are having
he/she/it is having
we are having
you are having
they are having
Present simple( or simple present):I have//You have//He/She/It has//We have/You have/They have
Present perfect I have had// you have had// he/she/it has had// we have had you have had// they have had (aqui o had é p.participle )

Present perfect continuous: I have been having// you have been having //he/she/it has been having// we have been having// you have been having //they have been having

Past continuous: I was having// you were having// he/she/it was having// we were having// you were having// they were having

Past perfect: I had had// you had had //he/she/it had had //we had had// you had had //they had had

Past perfect continuous: I had been having// you had been having //he/she/it had been having// we had been having //you had been having //they had been having

Past (simple): I had// You had// He/She/It had // We had// You had//
They had

Future ( simple): I will have// you will have //he/she/it will have// we will have you will have //they will have

Future continuous: I will be having //you will be having //he/she/it will be having// we will be having// you will be having //they will be having

Future perfect: I will have had// you will have had// he/she/it will have had //we will have had// you will have had //they will have had

Future perfect continuous: I will have been having// you will have been having// he/she/it will have been having// we will have been having// you will have been having// they will have been having

Infinitive
to have
Imperative:
have //let's have

Participle
Present= having//Past had