First, pick a character you´d like to play.
Then roll up the stats at the Invisible Castle. Inv.Castle roller
Basically, Call of Cthulhu uses eight stats. STR, CON, SIZ, INT, DEX, POW, APP, EDU.
All stats, for this scenario, are 3d6.
You may roll three batches and pick the batch you like the most.
Any roll below 7 is viable for a reroll.
Skill point allocation: EDU x 20 = Professional skills, INT x 10 = Hobby skills
Rules-wise you can read a quick-start from here: Rules QS