If a composite glyph is made out of glyph members that all contain anchors meant to position the individual glyph members, then auto attach will do all the magic for you. Right-click one or more glyphs in the Font panel, and select Auto Attach -> Enable.

 

The order of the glyph members is important, as mark glyphs must come right after a base glyph. If the base glyph is not the first one, then select it, right-click, and select Order -> Bring to Front. Alternatively select Custom Formula from the Edit menu, to adjust the order of the glyph members through the formula.

 

If your glyph is a ligature with marks, do ensure the Glyph OpenType Type as available on the Glyph Properties panel is set to Ligature and has the correct amount of ligature components.