I recommend you buy the Sand Filler that has the sand already in it. The only 'trick' is to leave the buckets in the sun (the day/night before), and in the morning, start stirring and pouring. EACH time you pour some out, you want to stir it. Again, READ the directions in the store BEFORE you buy to be sure you have all the right materials for the job. This type of Sand Filler is for cracks that are no wider than 1/8", nor deeper than 1/8". You'll need to fill them w/plain, old sand if they're deeper than that. (Just broom the cracks w/sand until you get them 1/8" deep.)
Beyond that 'dimension', you'll need a different product. My best to ya and hope this helps.