I DON'T want to go to the cinema TODAY to see this film because I HAVE already seen it. I DIDN'T want to go to the cinema YESTERDAY to see that film because I HAD already seen it. 'have seen' relates to now or a time period up until now, 'had seen' relates to a time period up until a point in the past.

The examples that Su.Ki. used are in present perfect tense and in past perfect tense, respectively. These are just two of the tenses used in English. This is not a simple short subject that can be answered here. In order to understand and learn them, you really need to look for proper lessons online explaining English tenses.

"I have seen the film" is used in the present tense, and "I had seen the film" is used to describe the past tense activity.