DWORD dwDriveBitMask = GetLogicalDrives();
The result is
dwDriveBitMask = 116
on your machine.
What you do is to convert it to a binary sequence. This is the bit mask.
MSB LSB
116 = 00000000 00000000 00000000 01110100 (DWORD has four bytes)
As the three upper bytes are 0, we can ignore them in this case and list the lowest byte only.
LSB 0 -> No A drive
0 -> No B drive
1 -> Have C drive
0 -> No D drive
1 -> Have E
1 -> Have F
1 -> Have G
0 -> No H
Then there is the matter what you want to do with it. As you don't tell us that I will just give a small example.
Let's say you want to check if drive F is present on the PC.
Then you need to mask out the bit that represents the F drive. You do this with the bitwise AND operator &.
First you need a test mask where only the bit for the F drive is set
00100000
then you AND the values
01110100 & 00100000 = 00100000
In C++ the code will be
DWORD dwDriveBitMask = GetLogicalDrives();
DWORD dwMaskDriveF = 0x20 (00100000)
if (dwDriveBitMask & dwMaskDriveF)
{
}