Learn Spanish (Latin America): Reciclen el plástico en los contenedores azules. - Recycle the plastic in the blue containers.

This is the ustedes (you all) command form. To give a group instruction using a regular -ar verb like reciclar, you swap the normal -an ending for -en. If you were just stating a fact ('You all recycle'), it would be ustedes reciclan, but as a command, it becomes reciclen.

Why is it contenedores azules instead of contenedors azuls?

In Spanish, if a noun or adjective ends in a consonant (like the r in contenedor or the l in azul), you make it plural by adding -es instead of just -s. Since both words describe multiple containers, they both need the -es ending to match in number.

Why is there an accent mark on plástico?

The accent mark shows you exactly which syllable to emphasize when speaking. Words that end in a vowel normally stress the second-to-last syllable (which would sound like plas-TI-co). Because the stress actually belongs on the first syllable (PLAS-ti-co), it requires a written accent mark to break the rule.

Can the word en mean both 'in' and 'into'?