Yes you can take them at the same time, but not in the same syringe or the same exact injection site. You would usually take the Humalog a little before (or same time) as eating carbs/meals, and/or to correct a high bg. Lantus is usually taken either in the morning or at bedtime (and sometimes split into 2 doses per day). I think I scanned another post about you taking Lantus already, but just getting the Humalog, correct?
Do you have a ratio for how much Humalog to take for a certain amount of carbs? (example 1 unit for 15 carbs). And a ratio for how much Humalog to take to lower a high bg? (example 1 unit lowers bg 50 points).