First you'll need a license for Audio Conferencing, this is included in E5 or available separately as an add on. This provides toll number dialin to Teams meetings. To add toll-free on top of this you need to buy Communication Credits as there is a charge per minute for use of free numbers. The rates are dependent on many factors, but you can download the price from https://products.office.com/en-gb/microsoft-teams/voice-calling.
There's nothing special you need to do to use Teams to meet with external people. When a user schedules the meeting, they just enter the email address of each participant. The recipients will be able to join using the link in the meeting invitation whether they are internal or external.
@Steven Collier is correct that Audio Conferencing is what you need to have participants be able to dial in to a meeting. The documentation about it is here. You will see there are two types of number that can be used to dial in: dedicated phone numbers and shared phone numbers. If you want a "toll-free number" (e.g. a 1-800 number in North America) you need to obtain a toll-free Service Number and assign it as a conference bridge. Since toll-free numbers have a per-minute cost associated with them, you also need to purchase Communication Credits to fund it.
However, when you say you want people to be able to dial in "toll free, globally", it sounds like you're looking to use the shared phone numbers Microsoft makes available world-wide. Again, there is nothing special you need to do here. In the meeting invitation, the number shown will be the default number assigned to the meeting organizer, but there will also be a "Local numbers" link that the recipient can use to see the list of the shared numbers.
As for hardware for a conference room, the Polycom equivalent for the "spider phone" that works with Teams would be the Trio 8500 or 8800. There are similar devices from other manufacturers. Here's how they work: you may be familiar with the concept of a "room mailbox", where a meeting organizer can book a meeting room by adding it to the meeting invitation. When you have a Teams-compatible conference phone, you sign in to the device using this room mailbox. When the meeting organizer schedules a Teams meeting and adds the room mailbox to the meeting invitation, the device receives the invitation. Then, at the scheduled meeting time, a "Join" button appears on the device's display that allows the meeting organizer to connect to the meeting.
Note that the Trio is an audio-only device when used with Teams. If you want to have video as well, you will want to look into a Teams Room solution.