i confused i not tried split before, what db do i need

i looked on google but still unsure. I wanted know if it will definatly work and what spillter are ok as expect lots people done it. I got a super hub and says 3.6db and 4.0 db on splitter, unsure if tv box or router is which not traced cable as a mess ha. i wanted buy a 3 way splitter to add 20 metre of virgin type cable and i was going to buy a cheap v box for bedroom, will this work? and what splitters will work need for the three on it. I didnt want pay extra so thought id see if this will work i not to up on tv cable only just got a package a while ago. It just the cisco basic tv box. Also will the card in it work or will i need use my card from lounge.
If anyone done all this appreciate advice.
Thanks
