Uploading to Specific Folder in Dropbox or Creates It

1. Yes, when uploading a file, you specify the full path where you want to upload it, including any parent folder(s). It sounds like you're using the JavaScript SDK (but please let me know if not), so for example, you would specify the 'FilesCommitInfo.path' value when calling filesUpload, or if using upload sessions, likewise in the nested 'FilesCommitInfo.path' values when calling filesUploadSessionFinish or filesUploadSessionFinishBatch.

For example, to upload a file named "example.doc" inside a folder named "documents", the path value would look like: "/documents/example.doc".

2. Yes, you can create folders using filesCreateFolder or filesCreateFolderBatch. 

3. You can use filesGetMetadata to see if a particular item already exists. Or, you can use filesListFolder/filesListFolderContinue to list the contents of a folder, to see if any particular item(s) exist inside it.