You'll need to apply for a visa in order to travel to Algeria, but a shoplifting record should not be an issue, assuming you're not on probation.
no you don't need a visa to go to Algeria
Your friend has to apply for a visa at the US embassy/consulate in Algeria.
It depends- if it is recent then yes, it would probably result in a rejection. If it was 20 years ago, then it probably wont affect your chances.
yes it is but the person in Algeria might have some trouble with the visa
Yes it does, because they show that the person dos not have good moral character.
yes
If you have an actual criminal record, then it is likely that you will be unable to get an Australian entry visa. Whether you have a criminal record will depend on whether your state considered you a minor at 17 or not, and whether you are still legally a minor now.
You can get but deposit 3000 euro in Crédit Populaire d'Algérie (CPA) www.cpa-bank.com
They would be treated and processed the same as any other criminal. The only exception would be that - if (or when) they applied to return to the UK, their criminal record would be available for immigration to see. It would then be up to the immigration service to allow or deny them re-entry.
can i return to US with five years visa
you may need to provide a police clearance for the job, but not for the visa. I'm not sure what a "caution" is, but if it doesn't show up as a conviction on a police record, then there's no problem.