how to use variables in mws?

i am studying mws, i want to use vairables, but i don't know how. pls tell me. thanks .

go to
Edit -> Parameters ->

In Edit-->Parameters add your parameters with values.
When building object, don't write numbers but use your defined parameters.
You can change objects dimensions via Edit--Parameters directly as well as use variables for optimization

Dear eirp! can you explain also how is it possible to apply variables for manual mesh generation? For example, now i use insertion of two fixpoints based on variables and some (~100) intermedia points betweent this two. But when i try to change variables, a new mesh generation failed with message " The specified fix point does not exist" . So, i use such way as manual correction of *.mod file to fix this problem by replasing constants to variables in the intermedia mesh generation operator ( '@ intermediate fixpoint between (5, 190, 6), (-5, 120, -4)) and this work, but i think this way is not right. Do you have any another solution ? My MWS is v.4.2
Thanx.