Hi,
This is my first post,so hello to everyone.I'm new to crypto(actually i'm interested in it),i would like to know what exactly a Bit mean? for example 128bits,1024 bits etc.
Thanks

Maybe try to use what is written in your signature.

8 bits = 1 byte

eg: 2 decimal = 00000010 binary

so 128 bit = 128 / 8 = 16 bytes

Bit = Binary Digit
a Bit value can be 0 or 1

In crypto, 128 bits is a common size of a private key (eg, AES, RC4), whereas 1024 bits is a common RSA public key size.

I'd rather say that 128 bits is a common size for an symmetric key, while 1024 bits is a common size for a private/public asymmetric key.