If you are using public transportation the SF Caltrain Station is one block away on the corner of 4th & King Streets. Also the N-Judah and T-Third Street Muni bus lines stop outside the Caltrain station at 4th and King Streets and in front of AT&T Park on King Street between 2nd and 3rd Streets.
If you are driving, there is visitor parking available in the China Basin Garage (entrance off 3rd Street right across from AT&T Park). Weekday parking rates are $5.00 per 20 mins, or $25 maximum up to 12 hours. Be aware that parking rates may change during game days.
Or better yet, take a Lyft!
Once you've arrived, head to Lobby 4, walk through to the outdoor walkway and then head left to Lobby 2. Take the elevator up to the 5th Floor and check in.