I thought that the ´dik´ and ´en´ endings indicated object and subject participles? How do tenses come into it?  I´m confused now.

Adam, they have tense characteristics as they they come from verbs.

Lets see some of them  ;

Past -dik [The verbal adjectives formed of -dik can carry both tenses though [past - present]

Kestiğin ekmek [ The bread which I cut [sliced]

Here, it is verbal adjective since it describes the noun [bread]

The action of slicing the bread was performed in the past. Therefore, it has tense which is past.

Kestiğin ekmeği masaya koy.

Put the bread you sliced on the table.

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 * Sevdiğim arkadaş ---> This may cause confusion, since, this type of forms with -dik participle can indicate the present.

 The friend I love [like] ---> The friend I  love now , not only in the past. So we need the whole context to decide.

Ece sevdiğim bir arkadaştı.  ---> Ece was friend of mine whom I loved [liked].

From the sentence above, It is not very clear that if the speaker  still loves his friend or something else happened and he changed his mind about loving his friend.

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 Present Participle -en

Yürüyen adam  ---> A man who is walking

The action of  walking is happening at present moment.

Yoldan geçen adam ---> The man who is passing the street.

Yoldan geçen adamı tanıyor musun  ? ---> Do you know the man who is passing the street ?

The action of his passing the street is occuring at present time.

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However, it may also indicate the past due to the context ;

Açılan fabrika

Geçen hafta açılan fabrikayı gördün mü ?

Have you seen the factory which was opened last week.