How can I convert binary into multiple 7 segment displays
If you're doing this with discrete IC's, like 74xx series, you need a binary-to-BCD converter. Searching on that phrase turns up the DM74185 [http://www.utm.edu/staff/leeb/DM74185.pdf] (the companion DM74184 goes the other way). BCD is Binary Coded Decimal -- 4 bits per digit, encoding 0-9. Then the outputs of those can go to BCD-to-7 segment converters, to the display.

For a 3-digit display (0-999), that's 10 binary bits, and you would need 5 or 6 of them. The data sheet shows how they get cascaded together.

However, further search on those part number comes up a little light, so those chips might not be common anymore. 

In modern times, you would build a calculator with a microcontroller. But if you want a hardware learning experience, you could do this on an FPGA, like the Go Board [https://www.nandland.com/goboard/introduction.html]. You would use Verilog or VHDL to describe the circuit you want. It's not like programming a microcontroller; you're describing a circuit that gets "wired up" in the FPGA, just as if you built it from gates.  But there is a significant learning curve for the tools and methods.