Those are really, really awful Omaha 8 hands. You can only use 2 of your hole cards for a low pot and hi pot but you can use a single card to qualify for both a high and a low. A common example is if you have A2xx and the flop comes 345 and that's the easiest example I can think of a low card (the Ace) qualifies for both the low (A,2,3,4,5) and high hand which is an A-5 straights or also called a wheel.
What happened in your example is the opponent uses JJ to beat your pair of 4s for the high hand then they tie you with a A {2) 4 {5} 8 low to split the low pot. So they take the HI POT and they chop the bottom pot with you. We call what happened to you getting "quartered" since you only won 25% or 1/4 of the entire pot.
The easiest way to make you understand that you can ONLY USE 2 CARDS IN OMAHA 8 is YOUR LOW IS DETERMINED BY A 5 CARD LOW. 2 IN THE HOLE AND 3 ON THE BOARD. Its the same with the hi hand you can only use 2 cards.
Daniel Negreanu has a video "How to Play Omaha Hi -Lo" on youtube that's the limit version and its straight forward stuff that everyone should know. I haven't watched it all the way through but I bet that if you followed his advice and actually practiced what's preached in that video then you would be a much better player.
Omaha 8 is a more complex game than regular Omaha because it involves a possible low so if you want to get better at omaha8 then you have to get better in Omaha is the best and most simple advice I can give you. And if you ask "How do you get better at that?" then I'll bet Daniel has another simple to understand video to get you started, lol.
For more playing time you can follow this advice:
Play the PLO8 freerolls on ACR is my recommendation. You high and low hand is shown as well as you play, so you cant miss anything. You will get a good feel for the game that way and without risk.
GL.
And I know
pokerstars has playchip sit and goes with the limit version 6 handed going frequently. DO NOT PLAY NL OMAHA 8 because you will not learn much from the experience as the games will be a bingo session at best. Practice discipline and working on starting hands and play limit or Pot limit.