Step by step as requested... (although this is from memory as I don't have the software to hand)
- Place your image/silhouette in the background of your view port (there are millions of tutorials for this google is your friend)
- Create the plane - Command Panel > Standard Primitives > Plane > Click and drag in the view port to create it - make it a bit bigger than your silhouette.
- Look in the Plane's Stack (or modifier list) and make sure the plane is made of 1 width and 1 length segment.
- Right click the name of the plane - and select Collapse to editable poly.
- With the object selected press Alt + X - this will turn the object semi-transparent so you should be able to see you view port image.
- Open up the editable poly and proceed to use the edge tools to slice, connect and cut the plane so that you have more vertices (remember keep 4 sides polygons ), then push and pull the vertices so they follow the edge of your silhouette (this doesn't need to be 100% right as the later steps will be harder if you over do it at this stage)
- When the silhouette is complete select poly mode, and select all the polygons and press extrude.
- Adjust the 3D block so that it looks correct in terms of depth and proportion.
- Apply a mesh smooth modifier to your stack, you can increase iterations to get a smoother appearance but I wouldn't go over 3 unless you have a really powerful computer.
- Then with the 'Show End Result' button selected you should be able to go in to the editable poly and edit the shape in real-time to get a more desired finish. Again you may need to add more geometry at this stage.
That should be it, but what I failed to mention is if you want to use this for a game it will be horribly high-poly and will generally be inefficient to use in a game. Therefore it would be good to use this blob as a high poly mesh to then bake a normal map onto a lower poly mesh - again google is your friend here too.
I would create plane then add geometry trace the silhouette, always
maintaining quads, then extrude. Adjust the depth accordingly, then
add a meshsmooth modifier, this may/will destroy a lot of the shape
depending on how you have distributed the geometry, you can either add
more reinforcement loops or adjust the shape in real-time using the