what are the data types?

Int
Char
Unsigned
Signed
typedef
byte


I dont know the ones in bold, can you explain me what they do?

Thanks.

Note that keywords and identifier names are case sensitive.

unsigned is the short form of unsigned int.
signed is the short form of signed int, which is equivalent to int.

typedef is not a type, but the keyword for defining new names (aliases) for types.

A char is one byte, but byte itself is not a type unless defined as such.

They are not data types.
Unsigned and Signed are modifier that tell you whether an int or a short can take negative values or not.
Typedef is used to created your own data types
There's no byte datatype, use char instead.

QuantumPete

For systems with tight memory, your modifiers for a variable signify how much memory that variable will consume on the system for storing data. A char is 1 byte = 8 bits as an example.