You mention chromatograms, so I'm going to assume that you mean Sanger sequencing, rather than NGS (though the answer is essentially the same).

You would end up loading double stranded DNA into the wells of your plate/strip for sequencing (PCR will amplify both strands since you'll have forward and reverse primers). You would, however, put in a single primer, which will only bind to one strand, in the sequencing wells. The resulting sequencing will be of a single strand and start a bit downstream of the primer.

Sanger sequencings isn't NGS, a chromatogram represents the average of the genome sampled. If a SNP is heterozygous, you'll see peaks for both alleles (they'll be shorter than homozygous peaks...you should be able to figure out why this is).

In general, it's helpful to picture what's actually happening in the tubes at the various steps (draw it out if that helps).