How subnetting works
An IPv4 address is 32 bits. The prefix length (the number after the slash) says how many of those bits identify the network; the remaining bits identify hosts inside it. A /26 keeps 26 network bits and leaves 6 host bits, so the block holds 26 = 64 addresses.
The first address of the block is the network address and the last is the broadcast address; neither can be assigned to a host, which is why a /26 has 62 usable hosts. The two exceptions are /31 (point-to-point links, RFC 3021: both addresses usable) and /32 (a single host route).
Wildcard mask
The wildcard mask is the bitwise inverse of the netmask (255.255.255.192 → 0.0.0.63). Cisco IOS ACLs and OSPF network statements use it instead of the netmask.
Quick reference
/24— 255.255.255.0 — 254 hosts/25— 255.255.255.128 — 126 hosts/26— 255.255.255.192 — 62 hosts/27— 255.255.255.224 — 30 hosts/28— 255.255.255.240 — 14 hosts/29— 255.255.255.248 — 6 hosts/30— 255.255.255.252 — 2 hosts