If you have a Gmail ID, you can use that to sign in on Google Adwords. It is as simple as that. Just use your Gmail ID, there is no need to create any ad campaign.
yes, it is so easy to sign up, just need have a gmail account, if you want to use "Ad campaign" you need read carefully suggestion there
Sign up is a first process in Adwords to start running your ads. So, yes, you can sign up first and then later create campaigns and ads.