How do TLR1/TLR2 activate the MyD88 dependent pathway
The TLR are usually working as homodimers (Toll-like receptors), although TLR2 can cooperate with TLR1 or 6.
Upon binding of its ligand (this is called pathogen associated molecular pattern) the receptors change their conformation and allow binding of TIRAP (TIR adapter protein) to their Toll-interleukin 1 receptor (TIR) domain. TIRAP then recruits MYD88, which then recruits IRAK1 or 4. The signal is then passed down the pathway as shown in the figure below (taken from the Wikipedia article on TLR).