Hello everybody!
I have been looking all around but wasnt able to find an answer.

I have RB951G02-HnD and other router (no idea if it has WDS - will check it later). The other router is MASTER (has got WAN etc.). I would like to connect mikrotik to this router via WiFi and broadcast master ssid. Is it possible?

Thanks!

No, Mikrotik will now work as a "wireless repeater" with other vendor's products. It will do it if both devices are Mikrotik.

Any ideas what can I do?

You will have to use two routers. One that is connected as a station and one that is acting as a bridge or you can use a product which has two wireless cards.

Sometimes wds could work with tplink or ubnt if atheros wifi is used in them. But it is with no guarantee and needs to be tested individually. To use single radio repeater is bad idea anyway.