You can enter ingredients into the recipe in whatever unit you wish. If your basis is pounds, you can enter 'x lbs yy z' and the program will convert it all into pounds. I often enter recipes which are in pounds as 'XX lbs' and let the program convert it into kg.
In terms of percentages, you can enter in all the grains (for example) and then click on 'grain pct' on the right hand tool column and adjust the percentages as you wish them to appear.
In terms of adjusting the grain bill or hop bill to your desired gravity, you can click on the slider for 'Est Original Gravity' just below the ingredient box and enter in your desired target OG. The grains will be scaled to achieve that target given your stated efficiency.
The same can be doing with hops, both adding them and them adjusting by desired IBU contribution and using the slider for 'Bitterness (IBU)' to adjust the total to your target.
