Schematic, not to scale — real side chains have specific bond lengths and angles; this is just a faster sketch (the fused rings in tryptophan and histidine especially are simplified). The shaded background behind each R group is colored by category: nonpolar chains fold inward, away from water; polar, acidic, and basic side chains tend to sit on the surface; aromatic rings can do both, and often stack against each other; glycine and proline are the two structural outliers you've already met — no side chain at all, and a side chain that loops back into the backbone itself. One flag worth knowing: histidine is grouped under "basic" here by convention, but it's a much weaker base than lysine or arginine — its ring is only reliably charged in a narrower pH range, which is exactly why it shows up so often at enzyme active sites.