I don't think he knows what you guys mean.
Anti-Aliasing is essentially like a kind of blurring device that softens edges to remove the "pixelated" look. If you've ever applied a pixel effect on your photos, you'd notice that the picture turns into an assembled bunch of colored squares. On a greater level --and more detailed so that it's actually "art"-- pixel art is a (time-consuming) process of creating "aliased" artwork.
How this "aliased" thing works is this: A usual little picture make take about 32 pixels high, 32 pixels wide. Imagine you're in MSPaint, disputedly the most accessible tool in pixel art development, and imagine you're setting the width and height of the canvas. There are no anti-aliasing programs in here (no auto-blur effect) that gives your pictures a pixellated feel. What you do is that you make a really small canvas, zoom in and draw a little picture out of pixels. Try a little man, or something, and then zoom out. When zoomed out, well-arranged pixels will work with each other to make a sprite or a piece of artwork.
tl;dr: Try making something in MSPaint or some other very basic program, since you're a beginner.
Lemme give you a list of keywords that people critique me with:
Palette - The number of types of colors used. Imagine all of the colors you used right next to each other. This is also a term for your color arrangement. You'll understand later.
Saturation - The contrast of the color. High-saturation colors are very bright. Most good works have slightly faded colors that are easy on the eyes. I can see the colors on the sign were done nicely, but the door can be less saturated. In you color palette, place the cursor in the "red" area and drag it a ways down to the gray area about half-way. There, you have a slightly faded color that doesn't strike against the other colors (Bright aqua and blinding lime green with painful bright purple and scorching hot pink. Yikes.)
Shine/Shade - Most good sprites can also have a light source. When brightening colors in lighter areas, turn up the contrast a bit and raise the "shade" of your color to a brighter look to make the shine appear significant. When adding shade to your character, lower the contrast (to make it less contrasting) and lower the shade of your color. Shadows can be anything, as long as it's dark enough to be seen.
Quality - The quality of the artwork refers to the restoration of your actual finish from the program's export. In other words, don't try to make a .gif out of MSPaint, for it will ruin your picture when it makes it. Quality normally doesn't describe talent.
Talent - The thing artists complain they don't have enough of.
+ Constructive Criticism - When someone says a good and a bad thing about your art and offers advice for fixing the bad.
- Unconstructive Criticism - When someone remarks about something bad about the art and offers no advice for it.
- Troll Crit - When someone says the entire picture is bad and refuses to explain why.
Always offer Construcocrits.
