Newbie fishing person here. Trying to catch some trout in Steel Lake (Federal Way, WA). Since I am unaware of the right technique, I observed how the other people are fishing in that area, assuming they know what they are doing.
Many anglers are fishing from the same spot — a floating dock pier, marked orange on the map below. They cast their spinning reels in the direction of the gray arrow which brings the bait/lure into waters that are 15-20 deep, marked green on the map. I also suspect there's a submerged tree in that area. The lake bottom has some (not too rich) vegetation and is a bit silted.
The anglers use a similar tackle setup: ~1 oz swivel bell sinker with a leader. Now, the leader length varies from person to person; the shortest one I saw was about 1.5' (45cm), while the longest was closer to 5' (150cm) which is seems to be a huge variance.
I noticed that after casting the anglers have their rods resting almost vertically, leaning onto the pier handrail. The important part here is that the line is straight, and the tip of the rod is slightly bent. These two things point to obvious presence of tension in the line. I understand that it allows the angler register the vibration as soon as the fish bites the bait.
When I cast my rod, the line just rests on the water surface, preventing me from knowing what's going on with the bait. If I try to get rid of the slack, I just move my weight (and the leader) closer to where I am.
What am I doing wrong and how to achieve the tension? Should I use a heavier sinker (1 oz instead of 1/4 oz)? Should I fix the drag on my reel?
If it matters, my rod's length is 6.9' (2.1m). It's medium power and light action. The line I use is 7.9kg test (came in the same kit with the rod).