I want to take a string from a textbox (txtFrom) and save the first word and save whatever is left in another part. (the whatever is left is everything past the first space)
You simply combine a split with a join to get the first element:
string[] items = source.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
string firstItem = items[0];
string remainingItems = string.Join(" ", items.Skip(1).ToList());
You simply take the first item and then reform the remainder back into a string.