Yes, there is a big difference. When you use anyone it is always plural, you are talking about more than one person.
Example, can anyone help me, means you are asking for help from a group of people more than one. If you say, can someone help me, you are asking about a specific person, one person. Someone who is standing close by and you don’t know them.
Example: Is anyone home? Means you are asking if more than one person is home because you don’t know how many live in that house.
You don’t say , Is someone home, because again you don’t know if only one person lives there and if you did you would say, Are you home?
Same thing goes for anything and something.
Example: get me anything. Means you want someone to get you whatever is out there. Be it food , drink, etc. anything out of many choices.
Get me something to eat or drink. You are being specific.
Hope I didn’t confuse you even more, English can sometimes be tricky. Hope I was helpful.