i get confused when i run with the suffix mis in a sentence.
could anybody explain it to me please!

check this
Mış
Also,you can use the search engine at the left side,and you will get many more result about mış,it's been discussed here many time before.
And i guess you would find it in the grammar section too.

But there is another use of -mış suffix, and it is when indicates an action already made: Ex: yapılmış.

There is a long discussion about -mış here natiypuspi,all she /he has to do is to search it and will find many topics talking about it in TC.

-miş is an interesting thing. The most common use is in reporting some action that you didn't witness yourself. It might be inferred (as in when you walk into a room and see that someone's cleaned it - temizlemişler). If you were to say "temizlediler" you would be saying that you were there.

Another use is to indicate secondhand information. If someone calls and tells you they're sick, you can then say to someone "so-and-so hastaymış." If you sayd "hasta" or "hastadır," you would be indicating once again that you saw that person sick.

-mış also functions as a perfective suffix; i.e. that indicating the present state as a result of something. We can say "pişti" for the food if we are talking its actual becoming cooked, but we can say that cooked food is "pişmış." This overlaps with the present perfect in English where we can say "it was cooked" or "it's cooked," the second being purely a statement of its present state. It's cooked, it's ready, and who cooked it or when is really irrelevant.

Another use that surprises people sometimes is to indicate "just learned" knowledge. For example, say someone has given you something to eat that you've never tried before. You can try it and say "ah, güzelmiş." If you said "güzel" or "güzeldir" you would be makıng a statement more about the inherent quality of the food itself rather than the fact that *you just tried and found it good.* You're just coming from visiting your mom, and someone asks "how was she?" - you can say "iyiymiş." Because you went not knowing, you found them and saw that she was well.

(-mış also functions as a perfective suffix; i.e. that indicating the present state as a result of something. We can say "pişti" for the food if we are talking its actual becoming cooked, but we can say that cooked food is "pişmış." This overlaps with the present perfect in English where we can say "it was cooked" or "it's cooked," the second being purely a statement of its present state. It's cooked, it's ready, and who cooked it or when is really irrelevant.)

'-mış' is used as an ending to make adjectives, too.
'Piş-' is an infinitive, and if we bring 'miş' ending after 'piş-' then we get a new word and we can use it as an adjective:
pişmiş yemek: cooked food ('pişmiş' is not a verb here. So we can't talk about overlaps with present perfect, I think)

The below examples also show the use of adjectives made with '-miş' ending.

okunmuş kitap
yazılmış mektup
tanınmış yazar