how to use a clipper

[Zannie]

my akitalab mix dakota is 15 years old and his fur has changed so much the last few years that its so hard to brush threw it, so we decided on the clipper we did some tonite and its coming of like sheep fur and that thick too .
it seems to take a long time to get threw a small part would i need a differant blade it came with one that you would use on a horses mane but his fur is alot denser any suggestions