Soler

Soler is an auxiliary verb, so you will always see it combined with another verb. It's used to indicate that an action is done on a regular basis. The only equivalent expression in English is "used to," which can only refer to the past tense, while the Spanish soler can be conjugated in several tenses. Of course, just as in English, Spanish has many adverbs that can be used to convey the same idea: usualmente ("usually"), regularmente ("regularly"), habitualmente ("habitually"), and so on, but the use of soler is much more common in casual conversation.

When using soler you must remember to always use proper syntax: you have to conjugate soler (the auxiliary verb) and then add the infinitive form of the main verb. English has a similar construction in the past tense (used + infinitive). Let's see some examples right away. And remember: if you see them highlighted in blue and you have an active subscription to Yabla Spanish, you can click on the link to watch the video containing the caption.

Después, suelo* lavarme los dientes en el baño,

After that, I usually brush my teeth in the bathroom,

y después desayuno.

and then have breakfast.

Captions 3-4, El Aula Azul - Actividades Diarias
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[*Suelo happens to be also a noun that means "floor"]

If we were to use an adverb to express the same idea, the construction would be different. Notice how the main reflexive verb lavarse changes because it needs to be conjugated:

Después, usualmente me lavo los dientes en el baño, y después desayuno.;p
After that, I usually brush my teeth in the bathroom, and then have breakfast.

In this example, Xóchitl conjugates the verb soler in the present tense (third person plural: nosotros) and leaves the main verb hacer ("to do") in the infinitive form, as per the rule:

... actividades que solemos hacer, eh, o festejar,

... activities that we usually do, um, or celebrate,

cada mes o cada año.

each month or each year.

Caption 10, Xóchitl - Vida en Monterrey
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But here, the band Pericos is talking about an action in the past, so the verb soler is conjugated accordingly:

Qué gano o qué pierdo yo así solías pensar

What do I gain or what do I lose that's how you used to think

Caption 17, Los Pericos - Fácil de Engañar
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Here is a combo (see, in green, a super literal English translation)

Después de comer, solemos echar la siesta

After eating, we usually take a nap

y mi padre suele ver la televisión.

and my father usually watches TV.

Captions 20-21, El Aula Azul - Actividades Diarias
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It is also quite common to combine the use of soler with an adverb reiterating the same meaning. So don't be too surprised if you see something like this: