There are TWO steps to doing laundry. The first part is washing it, the second part is drying it. I am fortunate enough to own a washer, so my explanation will be done under that assumption- for others you'll just go to an 'auto laundry' and do the same as home.
First off here's the 'weapons' against the dirt, we have some laundry soap and detergent. Make sure to get color safe, around 60 degree c max.
Pour in the softener...
Part II is a bit more time consuming.. you'll need one of these:
Jeans will be crispy and loose...
Still!! Better for the electricity bill. Good luck!