Yarn would have been spun from sheep wool or from flax to make linen.  To make yarn, some fleece was teased into a thin thread and attached to a weighted spindle. This was set spinning while the person doing the spinning teased out more wool into a thin thread. As the spindle dangled, the spinning trapped the wool together and made it into yarn. When the spindle hit the floor, the spinner would have to pick it up and spool the new thread onto the spindle, ready to go again.

When the spindle was full, it was set aside, until another spindle was full, Then the two yarns would be spun together to make 2-ply, a much stronger and more durable yarn that would not come undone. It took a long time to make enough yarn to be woven into cloth. For fine material, single ply could be used, but it would not last so long.

Linen is made from Flax. The plants are sown, tended and then harvested. They are laid in a ditch until the connective tissues rots. The long threads are then spun in much the same way as wool. They could make surprisingly fine thread.

Nettle was treated the same way, to produce a strong coarse thread, suitable for straps and sacks.

The Celts loved colour. The yarn would have been dyed. The sheep already came in various shades of cream through browns to dark grey. The darker colours would have to stay. The pale wool could be dyed. This was a complex process, readying the yarn to take the colour, preparing the various plants, roots, lichens, bark to make the various colours. The easiest were yellows and browns, but surprisingly bright colours of blue and pink were available, along with pale greens and purples. A bright red was hard to get, and a strong black was also difficult. 

Although this was the iron age, bronze was still useful. This belt buckle, a simple ring and boss, were useful, strong and versatile in either metal.

Here it is being used for a sword slung on the right hip. If needed the warrior could easily rearrange it to carry his sword on his back. This would be more comfortable for travelling, but it is impossible to draw the sword from this position. It would have to be moved, well in advance  of meeting any foe, to somewhere more easy to access., his right hip.

Carrying a sword was a sign of a warrior, someone of high cast and not to be trifled with.