How can you describe venomous snakes?

it's almost summer and here we have snakes like rattlesnakes(well we don't have all snakes known to man) but I wanna know how you can tell if snakes are poisonous...do they have spots lines stripes certain colors.....PS I already wrote this question but people needed to know where here is so "HERE" is California in a deserty place(used to be desert)...in my recent question I couldnt edit it so I made a new one