Schema map & relationships — Link two specific records

Most connections are best expressed as Relation fields — defined once on a table and filled in per record. For a genuine one-off between two exact records that no relation field covers, open a record's detail page and use Add a one-off link. Pick a Target record, give the link a Key (its connection name) and an optional Label, then press Add link. The new link appears under Manual links on that record, and the record it points at lists it under Records that use this — click either side to open the other.