Browsing the CATH database
You can start browsing through the CATH tree by starting at the least discriminatory classification level (Class) then working your way through to more discriminatory collections of domains ( Architecture, Topology, then Homologous Superfamily).
Searching the CATH database by ID/Keywords
You can search CATH with identifiers such as:
Searching the CATH database by FASTA sequence
You can perform a quick BLAST search of the sequences in CATH by submitting a FASTA sequence.