There are many ways, and shortcuts. One that always work is Office.com.
Start your web browser
Write office.com, press enter
Find the "Log in" button, click it
When asked, enter
Email-address
Password
A few tips and tricks
Use one of this web browsers:
Edge or Chrome (PC)
Safari works on Mac, iPad, iPhone (Edge/Chrome is OK)
Firefox do not support audio and video for Teams meetings, otherwise OK
Save password to minimize the number of times you need to login again (Microsoft will ask now and then for security reasons)
You will need to login more than once if you use apps such as Word, Excel, Outlook etc. Each app have its own "channel" and require login
Company connected computers may be easier to use, because you are already logged in to Office 365 in many sceanrios on those
Your username is nearly always your email, but not always
If you use two-factor login, you may want to read more about that here
Set a bookmark to https://office.com - to get back easy
Always save in Microsoft Office 365
So you are safe, not miss something
You can access all your files from any device
You can share files when needed
Store your personal files in OneDrive (företag)
Store files you collaborate with others on in Teams