For you to sign-up to Power BI, you need an organization access: Your organization should have a Microsoft account.
If you have this, there is two ways to start using Power BI: Using the Power BI Desktop, and/or Power BI Service:
Power BI Desktop:
Install and configure the Power BI Desktop – Straight forward from here:
Power BI Service:
You can also Sign-in/Sign-up to a new Power BI account:
If you try to use advanced features, like SSAS, Content Packs, Gateway, Groups, it will ask you to upgrade to Power BI Pro.
You can Try Pro for Free:
First time you apply this is once, then you are in the Power BI Pro subscription.
Then you will land to “My Workplace”.
Find next how to get data to start developing your reports.