With the big lumps of the C15 together, it's time to start detailing this model locomotive. For no particularly good reason, I started at the cab door.
The beading around the edge is supplied as 4 strips (2 for each side) which have a half-etched line along the middle. Simply line up the groove with the side of the opening, tack it in place and pus the metal around the inside of the hole.
I never bother with too much pre-forming, preferring a tiny bit of brute force to shove the metal where it is supposed to go. This works most of the time, especially on larger models. Solder inside the cab as you go and it will be fine.
On smaller stuff I'm normally tempted to leave beading off as being too fiddly to bother with. Maybe 4mm models justify it but in 3mm - well the etched parts are usually too small to use properly. If it's straight, fuse wire works well but to be honest, do it wrong and it looks rubbish. Better to ignore it for an easy life.