To Eat
To Drink
transitive verb, godan verb
You've learned that 召す can mean "to take" when a social higher-up takes a meal or a drink. Now you're adding 上がる (to go up), so you've got the added image of the food or drink rising up to their mouth. In other words, this is a respectful way of saying to eat or to drink.
This is a combination of the words 召す and 上がる that you've learned already.召す becomes 召し and then you add 上がる to it. Pretty straightforward, right?
もしよければお召し上がり下さい。
Please eat if you’d like.