double select ?

Hello,
building a online news system and want to show in a web page categories and articles that are related to those categories.
Table 1 Categories
Cat_name
cat_id

Table 2 Articles
Article Name
cat id

When the web page is displayed
Category Name (cat_id =1)
Article 1 cat_id 1
Article 2 cat_id 1
Article 3 cat_id 1
Category Name (cat_id = 2)
Article 1 cat_id 2
Article 2 cat_id 2
Article 3 cat_id 3

I can do each one separtly, but not a the same time,

any ideas

SELECT blahblahblah WHERE cat_id=1 OR cat_id=2

I don't have trouble writing select statements, what I have trouble with putting it all together..
I have two select statements
the first
select * from categories
while
echo "<tr><td> .$row["Cat_name"]. </tr></td>";
$finland = $row["Cat_id"];
select * from articles where cat_id = $finland;
while
echo "<tr><td>.$row2["Article_name"].</tr></td>

can anyone help me put this all together. Iam Oracle Web Dev, not much in PHP and wife needs help.