Using a RHEL7 machine, without GPT, I can see 3 primary partitions on a disk. The disk still has free space in the end. Question:How can I create 2 more partitions, a 512 MByte one, and a 1 GByte one? The last partition is at ex.: 13.7G ?If I create a primary partiton, then I cannot create any more. If I create an extended partition, I'm only allowed to create logical (?) partitions, but they are created with 1 KByte size!If I try to create a logical partition when there is only 3 primary partitons, it doesn't allows me to do it, only primary and extended is allowed. I suspect that I should create an extended partition, using all remaining disk space as the fourth one, and somehow, I have to create 2 partitions inside that extended partition so sum I will have my 3+2 partitions that I can use later. But how to do this using parted? 
If old MBR is used and there are already 3 primary partitions, how can I create two more partitions with parted?
parted
You need to print your partition table in parted to see the disk size and available space, thenmkpart extended 14029 15564will create an extended partition starting at 14029MB and ending at 15564MB (adjust both values to suit  I'm basing these on your 13.7GB and 1.5GB figures), andmkpart logical 14030 14542will create a 512MB logical partition inside the extended partition, and finallymkpart logical 14543 15564will create a ~1GB logical partition filling up the rest of the extended partition.(You should make sure your extended partition takes up all the available remaining space.)