My Rosetta Stone course is startin to introduce a new grammar subject. 

Bu pasta bu sabah yapıldı.

Bu fotoğraf ne zaman çikildi? 

Bu ev geçen kış inşa edildi.

So the new grammar concept is inserting this il/ıl right before the past. I´m confused by the meaning of this. If anyone knows what this means please let me know!! Thank you in advance.

Perhaps a few examples could help.

Bu pasta bu sabah yapıldı - the cake was made this morning

Bu pasta bu sabah yaptım - I made the cake this morning

Bu pasta bu sabah yaptı - He/she made the cake this morning

Okullar yapıldı - schools were built

Hello emilyp.

The suffix you are talking about is a passive suffix. You can use the passive suffixes with all tenses, but for detailed information on passive and the passive suffixes, please visit this thread: http://www.turkishclass.com/forumTitle_54824

Translations of your sentences (Please note that your 2nd sentence is not correct. The correct verb is çekmek, and not çikmek.):

1. Bu pasta bu sabah yapıldı. This cake was made this morning.

2. Bu fotoğraf ne zaman çekildi? When was this photograph taken?

3. Bu ev geçen kış inşa edildi. This house was built last winter.

I hope this helped. If you have more questions, do not hesitate to ask.

Actually, the second and the third sentences do not sound right to me. There should be an accusative suffix, like this:

Bu pastayı bu sabah yaptım.

Bu pastayı bu sabah yaptı.

As aurum has mentioned, these are examples of passive verbs.

Click here for another good explanation of passive verbs

Note the examples at the end of that web-page, where verbs end in a vowel, the passive version adds an ´n´ [beklemek becomes beklenmek], and where the verb root ends in an ´l´, like bilmek, the passive version becomes bilinmek.

I looked up some examples - I agree with you.

But now I don´t understand why we wouldn´t write:

Bu pastayı bu sabah yapıldı.

Perhaps just something we need to remember?

Quote from Wikipedia:

The accusative case (abbreviated acc) of a noun is the grammatical case used to mark the direct object of a transitive verb.

The direct object moves to the subject position in Passive sentence. So accusative suffix is not possible for it anymore.