Hi Kimberly 
Firstly, the “modelled” seam on clothing is a different thing from the UV Mapping Seams.
UV Mapping, flattens out the 3D object into a 2D square grid area,. which makes it easier to apply 2D textures.
When you define a UV Seam,. you’re selecting where the mesh will be split, so it can be flattened.
There are some standard, Pre-defined UV Mapping methods for standard shapes, such as Sphere, Cylinder and Box, or planar mapping, and there are different layout options for each type.
In the Modelling room , On the Top Right, there are three blue icons.
Modelling mode / Animation mode / UV Mapping mode.
Then there’s UV Unfolding ..(also called Pelt mapping, or UV unwrapping).
This is used when you have a complex shape, you want to be flattened out, and the seams you define on the object, help the program to flatten out the shape onto the grid.
Since this is a “Custom” option which would be used on a “non standard” model shape,.. there isn’t a simple guide to where you need to create the seams or add pins,.. it depends on the model, and how you want it split, and how you want it laid out on the UV template area.
for some clothing, you could simply define shading domains and apply a simple UV mapping pre-set like cylindrical, which would give you different areas where the colour / texture could be changed, by changing the shader / texture.
for example: a simple T-shirt would be split at the sides. and mapped with Box, or flat mapping
Once you’ve defined a seam, then you can hit the Unwrap button.
If it looks wrong,. you can go back and select another seam, hit unfold,.. until it’s right.,.. or close enough.
normally, when you Unfold,.. the mesh is split into sections (Islands) ...for example the front and back of a dress, would be split into two separate islands.
NOTE: this UV splitting does not effect the 3D model shape. it only effects how 2D textures and shaders will be projected onto the model.
Carrara isn’t great at automatically re-sizing and shaping these islands, but, with a bit of work, you can move, scale and rotate the UV layout to suit what you need. and, Yes,.. there are other programs which will do a better job of Unwrapping a mesh, and you could use those if it makes things easier.
Once you’re happy, you can export the UV “Wire-frame” template, by going to the Display tab in the modeller (UV Mapping mode) and clicking the “Export” button and selecting what size of image you want to export.
Then you can take that Wire-frame template into Photoshop, and apply textures on a new layer, to create your final texture map..
Other stuff .....
The Pro version is better, because the modelling tools (all the useful ones) are in the Pro version , ...not the standard.
With Photoshop,. you can work with a PSD image in layers,. and have that displayed on the model in Carrara, ..but you need to refresh the shader in Carrara to display any changes you make in photoshop.
Also,... Carrara has Layer shaders,. which allow you to create a shape layer directly on the model, like a rectangle, circle or oval, and apply a shader or texture to that area,. (like a design on a t-shirt), or a logo on a product box.
The Beta of Carrara 8.5 also has a “Multi-layer” shader, where you can create several layers with different textures or colours, and have different “blending modes” like Multiply, Add, Subtract etc,.. with sliders to control opacity of the layers.
Frank
I’ve used Max for DOS,. although it was called “Autodesk 3D Studio”, at that time 
Hope some of that helps
