I'm totally Newbie with meshing so i'll be so thankful to whoever will answer me on the questions below:-

First, what i have done is the following :
I opened SimPe, cloned “Musee Public Collection Sculpture” the 3 vase set, found under Decorative>Sculptures with their flowers, saved my package and exported its GMDC with the object's shadow. Then i opened Blender, imported the cloned object, meshed it but i don't know what to do next because my mesh contians 2 groups, the 3 vase set and the flowers , so do i have to add groups so i can UV map both of them together in UV mapper, or i have to UV map the vase set alone , then UV map the flowers alone ?

Second, I don't know how to UV map ? What's the type of map that i have to use for the vase set with flowers? Can someone tell me what is the perfect type of map that goes with all objects' meshing, or for each object i have to use a specific map type? For me , UV mapping is very diffecult which i can't understand

Third, how to make textures for the vase set and the flowers ? Each group must have its own texture ,or should i add both groups then make texture for both of them ? ? ?

I really need help here please.
Thank you so much.

I think what would help you most right now is the following links

Object Creation Tutorial
http://www.modthesims2.com/showthread.php?t=104795

Making Objects in Blender Tutorial
http://www.modthesims2.com/showthread.php?t=78555

Understanding UV-Mapping
http://www.modthesims2.com/showthread.php?t=79954

Everything you need to know should be there

Thank you so much Mystarria for your quick reply, but i've seen the 1st 2 links that you wrote to me, and they are not much helpful for me in this moment, because in the 1st tutorial , Lethe's using Blender for UV mapping, while i am using Classical UV mapper, and for the 2nd tutorial, by J Woods and Lethe, they are meshing one group of objects which is the table alone , while for me i'm meshing a 3 vase set with the flowers , that makes them 2 groups of objects. I don't know if there is any difference, while for the 3rd tutorial, i checked it , and it was soo helpful, but still didn't cover ALL my needs .

Purple Sheera,
for your problem specificly
if you want two different texture maps, two uv-maps and two mesh groups, you'll need to export the mesh groups from Blender separately and uv-map them separately.
This means: open up your mesh in Blender. If you already meshes them as two subgroups, go to the Object view, click on one subgroup and delete it, then export the other (call it 'flower' or whatever). Now press ctrl+z till you have both mesh groups again, then delete the other mesh group and export the leftover one (call it 'vase' or whatever).

If you haven't meshed them as two subgroups, things will get a little messy; You'll need to know what bits belong to which subgroups. You'll have to delete the vertices that belong to one subgroup in edit mode, then export the remaining mesh. Then open up your 'whole' mesh again and repeat the process for the other group.

Once you have your separate meshes, you can follow the tutorial procedures for uv-mapping and importing them.

Thank you so much Lethe_s , that helped alot and recovered all my meshing needs . But please what's the type of map that i have to use for the vase set and for flowers separatly ? And can you tell me what is the perfect type of map that goes with all objects' meshing (if it is possible?), or for each object i have to use a specific map type?