Start with productive intervals
Team & capacity shows each person's weekly working intervals. Choose Edit pattern to set working days, start/end hours and the break. A gap between intervals is a break; it is not available capacity.
Part-time days are data, not a special rule. Someone working Monday to Thursday has no Friday capacity unless their pattern says otherwise. Timeline display hours control the view, not the person's working hours.
Commitments reduce availability
Recorded calendar exceptions and recurring commitments reduce productive time. Normal weekly capacity is a useful summary before those reductions, not a promise that every hour is free.
A user account and a schedulable staff member are different. A meeting operator can have a login without consuming capacity; a staff member can be planned without logging in. An administrator can optionally link the two.
See absence and commitments, collaboration and user administration.