difference between SQLclient class and Oledb client

[Yangtsi River]

Hi,
I am using Access to practice database application developing, thus the
namespace system.data.oledb is used instead of system.data.sqlclient, which
is used for SQL server.
So the classes I used is also different, like oleddbconnection instead of
sqlconnection, oledbcommand instead of sqlcommand.
is there quite big differenct between this pairs of class ?

if there is no big difference, I could use OLEDB to learn , if there is ,I
have to use SQL Server from now.

Thanx.
Yangtsi River