After racking your beer off the cake be sure to leave a small amount of beer on top of the cake. Swirl up the yeast cake into suspension with the remaining beer liquid, sanitize the opening of your fermenter and pour the yeast and beer solution into a sanitized mason jar. Put cap on lightly and directly into cold fridge. Come back later and gently open cap to allow excess CO2 to disperse, then put cap a bit tighter on. Repeat last step 2-3 times and tighten each time a bit tighter with cap. All good. Try to use within 2 wks.
Best if repitched within 2 days.