Making a List of Parts?

Well, to get the number of elements in a table, you must you #Table, which returns highest numerical index in a table.

Also, to get only parts, you must do instance:isA'BasePart', with BasePart meaning all part classes.

Example script:

local Parts={};--// Table to contain parts.
for _,Object in next,workspace:children()do
    if(Object:isA'BasePart')then--// Gets all part instances.
        table.insert(Parts,Object);--// Puts the parts in a part table.
    end;
end;
print(string.format('Number of parts in the Workspace: %d',#Parts));--// Prints the amount of parts.

If you wanted to get every part in the workspace, even parts that are in models, you would have to use recursion.

Example #2:

local Parts do
    local Recursion;Recursion=function(Object)
        local Children={};
        for _,Child in next,Object:children()do
            if(Child:isA'BasePart')then
                table.insert(Children,Child);
            end;
            for _,Descendant in next,Recursion(Child)do--// Gets all the descendants.
                table.insert(Children,Descendant);
            end;
        end;
        return(Children);
    end;
    Parts=Recursion(workspace);
end;
print(string.format('Number of parts in the Workspace: %d',#Parts));--// Prints the amount of parts.

If you want to make a list of all the parts that are named a certain string, just have a table for containing them.

Example #3:

local Parts={};
do
    local Recursion;Recursion=function(Object)
        local Children={};
        for _,Child in next,Object:children()do
            if(Child:isA'BasePart')then
                table.insert(Children,Child);
            end;
            for _,Descendant in next,Recursion(Child)do--// Gets all the descendants.
                table.insert(Children,Descendant);
            end;
        end;
        return(Children);
    end;
    for _,Part in next,Recursion(workspace)do
        Parts[Part.Name]=Parts[Part.Name]or {};
        table.insert(Parts[Part.Name],Part);
    end;
end;
for PartName,arrayOfParts in next,Parts do

    print(string.format('Number of parts named %s in the Workspace: %d',PartName,#arrayOfParts));

end;

local parts = game.Workspace:GetChildren()
    for i=1, #parts do 
        if (parts[i].className == "Part") then 
            print(#parts)
        end 
    end

Use the number sign behind the parts when you print. And also do

for i=1, #parts do
if (parts[i].className == "Part") then 

To check if the thing in Workspace is a part.