Ah,thanks you pretty much mentioned the goal for my gaining. I'm trying to add only lean muscle,to fill out a skinny frame. I'm not looking to cut fat.
As was already mentioned, eat. Diet will be crucial. Look up any of the numerous TDEE calculators online and figure out how many caloires you'll need to gain lean mass. it's not an exact science, but it'll give you a general idea of what you'll need.
As for your workout, it really doesn't need to be complex. Generally, moderately heavy weights in the 8-12 rep range will be more conducive to gaining mass, but each person's body is different. Experiment and find out what works for you.
Compound lifts are the way to go. Learn to squat, back and front style. There is simply no better exercise for the lower body. Limiting yourself to the leg press is ignoring your posterior chain. Mix in some deadlifts (or Romanian deadlifts if you prefer) along with your leg curls and calf work and you'll have a well-rounded leg routine.
On your upper days you're doing more pressing work than is necessary imo. Drop the decline press (or just rotate it in and out with one of your other presses) and do some dumbbell rows to work your back more. Some laterals for your shoulders wouldn't be a bad idea either.
Personally, I like to change things up periodically. I may spend a few months focused on strength training; lifting very heavy in the 5 rep range. Then I'll switch (as I did just a couple of weeks ago) to lighter weights, more sets, higher reps, and much shorter rest between sets to really burn the muscles. This is a simple, alternating push/pull split, three days a week, which I'm really enjoying. Progress has been slow, but I can definately see the results in the mirror.