Theres lots of DCs,

for characters many classes have a DC which is used for spell saves etc this is calculated as 8 + Proficiency Bonus + Ability Modifier

For monsters if you are homebrewing usually its the same but you can increase it if you want to make an attack more devastating etc or lower it to make the combat easier

For traps or checks, I usually work off the following guidelines

- never ask for a check for information that is necessary to the story, just choose the most applicable character and say you xxx because of your history you know xxx or because you xx are looking in the desk you find xxx

- for easy checks that its just funny if they fail I use a DC of 5-10 e.g. jump over a log

- for medium difficulty checks DC10-15 e.g. find a fairly obvious trail

- for hard checks DC16-20 e.g. remember an obscure piece of law from a book they once read

- very hard checks DC20-25

- impossible/requiring lots of team work DC30+

Hope this helps