I tried to use a DisplayPort converter to HDMI but, it did not work. I have my monitor with DP port and my RP3 with a HDMI. I am confused about so many resources on the internet that do not provide a clearly response to my question. Can anybody explain me this?
DP - DisplayPort
The cheaper adaptors (in the £5 - £20 GBP range) are passive adaptors which are designed for DP output to HDMI input (the opposite to what you want/need).
There are active adaptors (in the £50 - £100 GBP range) that do the HDMI output to DP input. These typically need or come with a power supply.
You might want to try a HDMI to DVI cable if your monitor support DVI.