I would not recommend trying to learn jungle with Master Yi. While he scales quite well and his jungle clear is quick, his ganks are quite weak, he has very little utility to fall back on, and his early squishiness can doom you if you get set behind.
Jungling primarily focuses on three things:
- Farming (make use of the gold and experience to be found in the jungle, take efficient routes)
- Assisting allies (ganking, holding lanes, relieving pressure, providing/removing vision)
- Objective control (taking Scuttle Crabs, Dragon, Rift Herald, Blue Buff, Red Buff, Baron and towers)
I would recommend you begin learning the jungle using more durable champions (primarily tanks and fighters) which will allow you to fall back on defensive items when behind. I would recommend choosing champions with mobility and reliable CC to simplify ganking.
Focus on your decision-making more than your mechanics; that knowledge is applicable to every jungler.
Now, you seem to be level 18, which causes a few issues.
The biggest issue is that you don't yet have proper runes. Without proper runes, you will be clearing slower and taking more damage from jungle camps, which weakens you significantly.
I would recommend saving up your IP for the next few levels and purchase two basic rune pages:
Page 1: Flat AD Marks, Flat Attack Speed Quints, Flat Armor Seals, Flat MR Glyphs
Page 2: Magic Pen Marks, AP Quints, Flat Armor Seals, Flat MR Glyphs
These will cover pretty much every champion in the game somewhat adequately and will hold you until you can afford more runes and rune pages.
Since you are still learning the game, I would recommend choosing simple and straight-forward champions. I would recommend trying some of the following since they are all fairly simple to pick up, (somewhat) durable and cheap:

While you are learning, I would recommend you look at what more experienced players do.
Probuilds.net and Champion.gg are both useful web-sites for builds (masteries, starting items, final builds, etc).
I would recommend checking Youtube for recorded games with commentary. Streamers such as Nightblue (aka Rabia), TheOddOne, HuzzyGames, Stonewall008, Valkrin, Foxdrop are all experienced jungle players who typically provide useful advice during their games.