All account management and user data input is handled by your company's Motivosity administrator. If you are a new hire, typically your administrator will get you into the system after a week or two, so you should be fine to wait for the welcome email to come in.
If you are outside of that time period, you will find yourself in one of two situations. The first is that you do have an account created already, but you aren't sure or maybe you missed the welcome invite. (This actually happens to be the case quite often, so we would recommend taking a minute to check) You can test this quickly by going to app.motivosity.com to the login page, typing in your company email address, and clicking the 'I Need My Password' button. If you have an account, it will inform you that a link has been sent. If there is no account under that email address, it will also inform you.
In the event that you tried going through the step above, you are in situation two and don't have an account created for you at all. At this point, you will need to reach out to your administrator. You may know who this is off the top of your head, your manager and peers likely know who it is, but as a last resort, you can also find out by clicking the 'Create new ticket' button in the top right, or by emailing in to firstname.lastname@example.org asking to be connected with your admin.