Does spanish use l' like French?

In standard Spanish, people always write la before feminine words beginning with a vowel: la obra, la uva etc. If the vowel is a stressed a, they generally write and say el: el agua, el arma, el área etc.

When the word after la begins with an unstressed 'a', in normal speech, one of the as is elided in pronunciation. In other words la alfombra is generally pronounced l'alfombra, la antigüedad is generally pronounced l'antigüedad etc.

How do you tell whether to use el or la?

The definite article in Spanish (the word that generally translates English "the") depends on the gender of the noun. All nouns in Spanish are generally either masculine or feminine. In general:

certain endings strongly dictate the gender of a noun (e.g. nouns ending in -ión are practically always feminine; those ending in -or are practically always masculine);
nouns that refer to people— and certain common animals— tend to follow the gender of the person/animal they refer to;
there are a few arbitrary exceptions.

To choose between el and la, the first stage is to determine the gender of the noun. Then, the general rule is:

use el with masculine nouns;
use la with feminine nouns;
use el immediately before feminine nouns that begin with a stressed 'a' vowel (el agua).

The last item is the one that it's easy to forget. There are a very small number of other exceptions, some of which aren't widely agreed upon.

So the question of whether to use el or la essentially boils down to: how do you guess the gender of a Spanish noun?

Basic gender rules

The following are the most common patterns for telling whether a Spanish noun is masculine or feminine, and therefore whether to use el or la. Note that rules referring to endings typically apply to words of more than one syllable¹. So for example, whilst words ending in -ie are generally feminine, the word pie (="foot") is masculine.

1. Strictly speaking, they tend to apply when the given ending is a derivational suffix (an ending used to derive one word from another). But sometimes it's difficult to tell whether the ending is derivational or not, and "more than one syllable" is usually a good enough approximation.
2. There are some exceptions or cases of disagreement or geographical variation. For example, Butt & Benjamin give el champaña, but in Mexico at least, speakers appear to make champaña feminine (even referring to the drink), although the alternative el champán is always masculine.

Common exceptions

There are various exceptions to the above patterns, but the following are some of the most common: