How to make lines scalable...

I'm more of a "recreational" user of coreldraw, so there is plenty that I don't know!...

I'm hoping that this is an easy question for many...

Plain and simple... How do you make lines "scalable?"

I have created a project, but when all the elements are combined, and I try to scale the size up or down, the lines don't scale (I hope this makes sense)...

I'm hoping that there is an easy way other than continuing to change the line thickness every time I vary the size of the image.