To add a Relation in iD-editor:
1/ while on Openstreetmap.org : pick any way which will form part of the new Relation ;
2/ in the left hand pane, under All Relations pick the ’ + ’ ; an empty relation box appears ;
3/ start typing (in this example, I’m adding a recently signposted Cycle Route) : 'Cycle Route ’ (up to this point, the name of the nearest existing Cycle Route will be suggested) : just continue typing the proposed name of the new Relation ;
4/ a two-line ‘table’ appears, in de box below the name ‘Cycle Route [name of the new Relation]’ you’ll see ‘New Relation’ : click that …
5/ the sidebar content changes, click ‘Route Features’ > ‘Cycle Route’ ;
6/ add any relevant particulars such as : colour=red , distance=*km , name=[name of the new Relation] , route=bicycle , type=route and network=‘lcn’ or ‘rcn’ - as appropriate and conforming to loval and worldwide OSM conventions ;
7/ click the tickmark in the upper right hand corner of the sidebar / edit box : that’s it : Relation created.
In map edit view : pick the next way to add to the relation et voila, automagically the relation name you just created appears as top suggestion : accept and continue.
Any questions? Or a suggestion where to place these steps in for example the wiki or add it to LearnOSM/iD-editor Please let me know.