Can we submit (an updated version) of a work previously submitted to arXiv to a conference? Is this possible to submit a newer verion of a paper  submitted on arXiv (which was never submited to any conferences before), to a new conference and then update arXiv with the new version?
Yes. 

Assuming the conference doesn't forbid that (many don't). If it does, then just update the arXiv version before submitting to the conference (or before signing anything).