Issue with displaying vertical and diagonal letters - C Programming

Question

I'm totally new to C Programming and I'm trying to create a Word Search .

I've got a list of words , where only 4 are randomly picked. These 4 words than are to be printed in a grid horizontally, vertically or diagonally, however I can only get them to print horizontally. I also must add that I have no idea on how the piece of code works so I really appreciate if someone kind enough can actually help me. So can anybody help me in the right direction to create the random words in a vertical and diagonal alignment ? https://i.sstatic.net/3tk2b.jpg

void putHorizzontalWord(char word[10])
{
    int rRow, rCol , ok , i;

    do
    {

        rRow = rand() % 10;
        rCol = rand() % 10;

        ok = 1;
        if(rCol + strlen(word) < 10)
        {
            for(i = 0;i < strlen(word);i++)
            {
                if(puzzle[rRow][rCol + i] == ' ' || 
                    puzzle[rRow][rCol + i] == word[i])
                {
                    puzzle[rRow][rCol + i] = word[i];
                }
                else
                {
                    ok = 0;
                }
            }
        }
        else
        {
            ok = 0;
        }
    }
    while(ok == 0);
}

Answer 1

Here are some comments aimed to explain you what does that code does:

// This function takes a string as input then puts that string
// at a random "open" location in a 2D grid (puzzle) in an
// horizontal manner
//
// This function expects the size of the string to be at most = 10

void putHorizontalWord(char word[10])
{
    int rRow, rCol , ok , i;

    do
    {
        // Randomly select a location
        rRow = rand() % 10;
        rCol = rand() % 10;

        // For now, assume that this location is "ok", i.e. is open
        ok = 1;

        // Check that the word fits inside the grid from (rRow, rCol)
        if(rCol + strlen(word) < 10)
        {
            // If it does, then try to put the word at this location
            // Thus, we need to process the word character by character
            for(i = 0;i < strlen(word);i++)
            {
                // We are inside the for loop
                // The current character to process is word[i]
                // And the current cell to fill is (rRow, rCol + i)
                //
                // If current cell is empty || is same as the current character
                // then this cell is "open" i.e. we can use it
                if(puzzle[rRow][rCol + i] == ' ' || 
                    puzzle[rRow][rCol + i] == word[i])
                {
                    puzzle[rRow][rCol + i] = word[i];
                }
                else
                {
                    // The cell is not open
                    // => (rRow, rCol) is not "ok"
                    ok = 0;
                }
            }
        }
        else
        {
            // word not fits inside the grid from the location
            // => (rRow, rCol) is not "ok"
            ok = 0;
        }
    }
    while(ok == 0); // Exit loop while not found a good location
}

If you have understood, then you can now modify this to write your vertical and diagonal versions. If you still have not understood, let me know what is still not clear.