How to take calcium supplements for best absorption will depend on the type of calcium supplement you have: calcium carbonate or calcium citrate 
Calcium carbonate contains more calcium (40%) but requires stomach acid for absorption and should be taken with food.
Calcium citrate contains less calcium but is absorbed more easily and can be taken on an empty stomach or with food.
Regardless of whether you take the carbonate or citrate form, all calcium is better absorbed when taken in smaller doses (typically less than 600 mg). If you take more than 600 mg daily, consider splitting it into 2 or more doses during the day and taking with a source of vitamin C to improve absorption.
Additionally, take calcium supplements at least 2 hours before or after your daily multivitamin and any other mineral supplements (including magnesium, zinc, and iron) since they can compete with calcium for absorption.
Lastly, make sure you are getting enough vitamin D
, which helps your body absorb calcium. If you have low vitamin D or are not getting enough from sunshine and your diet, consider choosing a calcium supplement that contains vitamin D.