The AG chair should submit a group travel request, which estimates the expenses of each traveler. To fill out that form, your AG chair may ask you for your own estimates.
Then, once the group travel is approved, the AG chair will send you the group travel purchase order number, which you should include on the attached Travel Authorization Form. Please submit that form to your AG chair.
Once your Travel Authorization form is approved, you, the traveler, arranges for your own travel using the IHTSDO Travel Policy, which can be found here: https://confluence.ihtsdotools.org/display/TRAV/IHTSDO+Travel+Policy
After you travel and within 4 months of that travel, you will submit your expenses via email@example.com. See the travel policy and Where is the Expense Claim form? for more information.