Power transformer secondary 250-0-250, 3.15-0-3.15 3.15-0-3.15. How do I connect to circuit board to have 6.3vac?
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Two options: independent 6.3 V supplies or paralleled supplies for greater current. The 250 - 0 - 250 secondary is not shown.

Normally transformers like this have split primaries of 120 V each as I've indicated here. They're connected in parallel for 110 V systems and in series for 230 V systems.