Catalan nouns are inflected for gender (masculine or feminine) and number (singular or plural). There is no case inflection. Articles and adjectives agree in gender and number with the noun they refer to.
Usually, masculine nouns are unmarked, feminine nouns carry the suffix -a; and the plural is marked with the suffix -s, which makes the feminine ending turn into -e-. Here is an example with the word ‘cat’:
gat (masculine singular) - gats (masculine plural)
gata (feminine singular) - gates (feminine plural)
Catalan has two types of articles, definite and indefinite. They are declined for gender and number and must agree with the noun they qualify. As with other Romance languages, Catalan articles are subject to complex elision and contraction processes.
The inflection of articles is complex, especially because of frequent elision, but is similar to neighboring languages. Catalan has more preposition-article contractions than Spanish, like dels ("of + the [plural]"), but fewer than Italian (which has sul, col, nel, etc.).
A Catalan adjective must agree in gender and number with the noun it accompanies. Most adjectives are placed after the nouns. Adjectives can be divided into three declension paradigms. The number inflection rules are the same as the nouns.
For adjectives with distinct feminine singular form, the masculine is usually unmarked for gender and ends in a consonant. The feminine singular form of regular adjectives can be created from the masculine singular. Most times the feminine form is created by appending the suffix -a to the unmarked masculine form.
Degrees of comparison are expressed with a construction implying the adverb més "more" or menys "less":
Sóc més alt que tu - I am taller than you
Catalan adverbs, like their English counterparts, are used to modify adjectives, other adverbs and verbs or clauses. They do not display any inflection; that is, their form does not change to reflect their precise role, nor any characteristics of what they modify.
In Catalan, most adverbs are derived from adjectives. In most cases, this is done by adding the suffix -ment (like "-ly" in English) to the adjective's feminine singular form. For example, the feminine singular form of lent ("slow") is lenta, so the corresponding adverb is lentament ("slowly").
The morphology of Catalan personal pronouns is complex, especially in unstressed forms, which are numerous (13 distinct forms, compared to 11 in Spanish and 9 in Italian). Features include the neuter gender (ho) and a great degree of freedom when combining different unstressed pronouns (65 combinations).
This flexibility allows Catalan to use extraposition extensively, much more than French or Spanish. Thus, Catalan can have m'hi recomanaren ("they recommended me to him"), whereas in French one must say ils m'ont recommendé à lui, and in Spanish me recomendaron a él. This allows the placement of almost any nominal term as a sentence topic, without having to use the passive voice (as in French or English) that often or identifying the direct object with a preposition (as in Spanish).
Catalan verbs express an action or a state of being of a given subject and like verbs in most of the Indo-European languages, Catalan verbs undergo inflection according to the following categories:
Catalan verbs are traditionally divided into three conjugations, with vowel themes -a-, -e-, -i-, the last two being split into two subtypes. However, this division is mostly theoretical. Only the first conjugation is really used nowadays (with about 3500 common verbs), whereas the third (the subtype of servir, with about 700 common verbs) is used rarely. The verbs of the second conjugation are fewer than 100, and it is not possible to create new ones, except by compounding.
The grammar of Catalan follows the general pattern of Western Romance languages. The primary word order is subject–verb–object. However, word order is very flexible.
Commonly, verb-subject constructions are used to achieve a semantic effect. The sentence "The train has arrived" could be translated as Ha arribat el tren or El tren ha arribat. Both sentences mean "the train has arrived", but the former puts a focus on the train, while the latter puts a focus on the arrival.
Some of the most common Catalan prepositions include: sota, fora, dins, amb, de, a, com, per, sobre, etc.
This is a very brief overview of Catalan grammar. To truly master it, you will need to study each of the parts of speech in much more detail. However, this overview will hopefully give you a general idea of the Catalan grammatical system and of the main points you should consider when learning.