Do you mean that you don't understand the difference between 'bored' and 'boring' , or 'interested' and 'interesting'? If so, the answer is quite simple.
It helps to remember that words such as 'interest', 'bore', 'frighten', 'amaze' and 'fascinate' are verbs. Verbs have two participle forms:
1. present participle, which ends in 'ing'. This is the equivalent of '..endo' and '..ando' in Spanish.
2. past participle, which in regular verbs ends in 'ed'. This is the equivalent of '..ido' or '..ado' in Spanish.
Things such as films, books, stories, school subjects, (and other people) can interest, bore or excite you, because you find them interesting, boring, exciting,and so on.
As a result, you feel interesting, bored, excited, amazed etc. This is a passive form, and it indicates your reaction.
For example:
This book bores me = This book is boring = I'm bored (by the book)
The film interests me = It's an interesting film = I'm interested (in this film)
I hope that helps.