You can tell Skyline which replicates are your Standards and which are your Unknowns by using the Document Grid.
Use the menu item:
View > Document Grid
to bring up the Document Grid, and then choose "Replicates" from the Views dropdown at the top of the Document Grid.

The Replicates view in the Document Grid has a "Sample Type" column which you can set to "Standard" for your external standards, or "Unknown" for the replicates that you want to quantify.

You can also fill in the "Analyte Concentration" for your external standards.

You can tell Skyline how to do the linear regression through your external standards by going to:
Settings > Peptide Settings > Quantification
You can also choose the regression weighting ("1/x" etc) on that same peptide settings quantification tab.

For more information about calibration curves in Skyline you can take a look at the Absolute Quantification tutorial:
https://skyline.ms/_webdav/home/software/Skyline/%40files/tutorials/AbsoluteQuant-3_5.pdf
and there are some links to other relevant webinars here:
https://skyline.ms/wiki/home/software/Skyline/page.view?name=tutorial_absolute_quant

When you have your calibration all set up correctly, you can see the calculated concentration in the Document Grid. The built in view "Peptide Ratio Results" will show you the calculated concentration, or you can find it in the View Editor:
Proteins > Peptides > Peptide Results > Quantification > Calculated Concentration

(If you want more information about the Document Grid, take a look at the Custom Reports tutorial: https://skyline.ms/wiki/home/software/Skyline/page.view?name=tutorial_custom_reports )