can some one please explain the difference between dim and digim

dim is past tense (I)

is digim also past tense (I)

and if so when do you use each one

thanks in advance

I cant explain but give an example

Mavi otobüse bindim: I got on the blue bus

Bindiğim otobüs maviydi: The bus I got on was blue.

Eve gittim: I went home

Gittiğim ev arkadaşımındı: The house that I went was my friend's

I hope that helps

And "diğim" isnt necesarrily past time all the time

Benim gördüğümü sen de görüyor musun? : Do u also see what I see?

Yürüdüğümüz yol çok güzel: The road we are walking on is beautiful.

1) -dim
is the 1st person singular past tense form.

i.e.
geldim - i came
aradım - i called
yaptım - i did

this is subject to vowel harmony.

2) -diğim
is the 1st person singular object participle form.

this is usually called the -dik object participle, but it is usually used with a personal ending (i.e. -im, -in, -i, etc.). and as we know in turkish, usually when -k- is between 2 vowels, it becomes -ğ-. which is where you get the -diğim.

the -dik object participle means "that" or "which".

i.e.
okuduğum kitap - the book that i am reading/the book i am reading

çaldığın araba - the car that you stole/the car you stole.

remember the -dik object participle is also subject to vowel harmony.

i.e. -dik, -duk, -dük, -dık
-tik, -tuk, -tük, -tık
-diğim, -duğum, -düğüm, -dığım

there is some more explanations and examples here:
http://www.turkishlanguage.co.uk/objectpart.htm

if we take incişka's examples:

Bindiğim otobüs maviydi: The bus that/which I got on was blue.

Gittiğim ev arkadaşımındı: The house that I went was my friend's

Yürüdüğümüz yol çok güzel: The road that we are walking on is beautiful

thank you both so much... that was very helpful I understand it now.... I will go and practice