For the development of the communicative skills, grammar is as much necessary as the knowledge of words. The lexicon is necessary to give meaning to the message of communication. So teachers must emphasize the importance of the study of the lexicon from the first class, because it is a slow and complex process that needs effort.

Teachers must give instructions upon how to imply strategies of learning that demonstrate how to relate the words, how to use them appropriately in a given context. In other words, teach not only words, but also lexical units. The words are related one to others within different semantic fields. Therefore, on having learned lexicon, we must relate expressions to others to assure its storage.

But what does it mean to know a lexical unit? In the following analysis we implied as fundamental the viewpoints of M. Higueras (2008; 2009) and D.M. Ugarte Maíz (2013).

1. Pronunciation and spelling (the form): to recognize, to be able to pronounce and write the word.
2. Morphology (structure interns): to know the forms: prefixes, suffixes, derivations, compositions.
3. Syntax (the use): to use it in a context.
4. Semantics (the meaning): to know the different senses: denotative and connotative meaning, figurative sense, metaphorical uses.
5. Pragmatics (the concept): to use it for different intentions.
6. Sociolinguistics (the register, frequency): to know dialectal forms, frequency of its use.
7. The cultural content.
8. The syntagmatic combinations (the associations): what other words make us remember the word?
9. The belonging to institutionalized expressions.

To realize all these proposals we can choose between several methods. Moreno Ramos (2004) distinguishes four types of the activities: conventional, playful activities, input-activities and of dramatization. The conventional activities are the traditional ones. There are few contextualized and they are quite mechanical. For example: to classify, to relate words to its definition, to set in alphabetical order, to indicate synonymous or antonyms.

For example:
The context of the playful activities depends on the task but they are provided with a cooperative work and with an agreeable ambience due to the game (all kinds of games). The game creates another more familiar ambience in which the pupils feel more relaxed and it motivates them to use the language puts. This type wakes up the creativity, breaks the monotony of the revisions and, also, contributes to the spirit of the group.

For example:
The input-activities are based on the relations of the lexical units. For example associations, mental maps, rain of ideas. Namely to produce words from a generating input. On the other hand, these tasks are very good for the preparation of a written or oral vocabulary exercise.
With the dramatization activities we integrate the lexicon in the verbal and not verbal language (to put in scene the situations). With the gestures and the mimicry the memorizing will be even more effective.

In conclusion, it is possible to say that at Spanish lesson there are no learned words but only lexical units, which need to be considered from different aspects, not only linguistic. To facilitate the learning process, the teacher must select precisely the taught lexicon and present it across creative activities that assure the storage in the long-term memory.

Keywords: Spanish as a foreign language, lexical units, activities, competence.