A repeater directory is a list of repeaters with the details you need to use them: where they are, what frequency, what offset and tone, and what mode. Nobody memorises them. You use the directory once to find a repeater in a new area, then store it in a radio memory. This article describes the kinds of directory, not any one service: contents and availability change, so read each one's own documentation.
What a listing contains
Illustrative listing (not a real repeater). Always confirm by listening.
Field
Meaning
Output frequency
what the repeater transmits: the frequency you listen to
Offset
the shift from output to the frequency you transmit on, as a direction (plus or minus) and an amount
Access tone
a CTCSS (PL) tone your transmission must carry, or a digital code or talkgroup
Mode
FM, or a digital system such as DMR, D-STAR or Fusion
Location and coverage
the nearest town, site and approximate range
Access and sponsor
open to all, members only, or closed, plus the club or owner
Linking
whether it connects to others, by radio or internet
Standard offsets depend on the band: typically 600 kHz on 2 m and 5 MHz on 70 cm. In the example, 146.940 − 0.600 = 146.340 MHz is where your radio transmits. Details are in Repeaters and how to use them and Squelch, CTCSS and DCS.
Kinds of directory
Online databases that anyone can search by place, band or mode, often fed by owners and users. Some can export a file for your radio.
Printed and downloadable books from national groups and clubs.
Local frequency coordinators: volunteer bodies that assign repeater frequencies in an area so that repeaters do not interfere with each other. A coordinator's own list is the most authoritative source for that region, though it may not cover every repeater.
Club and group pages, which give access rules, net times and operating notes the big databases leave out.
Programming software, which often has its own import, search or download features.
Using them
Search by where you are or are going.
Check the date and the status. Repeaters go off the air, change tones, or become private.
Listen first. Hear the output before you transmit, to confirm it is active and to learn its etiquette. See Repeaters and how to use them.
Enter it correctly: output frequency, offset direction, tone. A wrong tone is the usual reason you can hear a repeater but cannot open it.
Respect access. A closed repeater is for members; use an open one, or ask.