There are a couple of methods depending on the result that you want.#
1 Draw a circle using the

tool (hold down ctrl to kep it to circles not ellipses)
2)use a pattern fill (select object, Object->Fill and stroke...)
3) in the fill and stroke dialogue, under fill select the pattern option
4)Under pattern fill select one of the stripes options
5) you can use the node tool (

) to adjust the pattern./ scale the pattern and rotate it 90 degrees.(look at the top left of the page border for the controls
Or:1 Draw a circle using the

tool (hold down ctrl to keep it to circles not ellipses)
2 Use the hatch LPE:select the circle, then go Path->Path effect editor. Select Hatches (rough) from the drop down and click add, experiment with the options
Or:1 Create the circle, go path-object to path
2 Using the node tool (

) select 2 nodes on opposite sides, click on the "break path at selected nodes" (4th from left on bar) to create 2 subpaths
3 select top node; go path->reverse.
4 Path->Path effect editor-> stitch subpaths effect. increase number of subpaths