Need to sign a message? Using S/MIME or PGP.
    Need to checksum a file? Use SHA256.
    Need to hash a password? Use bcrypt, scrypt, or PBKDF2.
    Need to transmit data over a network? Use HTTPS/TLS
    Need to secure HTTP? Use HTTPS/TLS, preferring AES in CTR and then CBC.
    Need to secure home WiFi? Use WPA2PSK.
    Need to encrypt files? Use any implementation of PGP.
    Need to do (this type) of encryption? Use PGP. Never use AES directly. Never use ECB for anything.
    Need to create a TrueCrypt volume? Can't help you; we use PGP.