Halakha Mazmur 84:5: Mishneh Torah, Prayer and the Priestly Blessing & Shulchan Arukh, Orach Chayim

In the afternoon service, the Reader begins reading: "And He, being merciful, forgiveth iniquity and destroyeth not; yea, many times He averteth His anger and awakeneth His wrath not at all" (Psalm 38, verse 38),^*This verse is not recited before the afternoon service but before the evening service both in the German and Spanish rituals. and "Happy are they that dwell in Thy house etc. A Psalm of David etc." (Psalm 145). While reading this psalm, both he and the congregation are seated. The reader rises and says Kaddish. The congregants rise after him and make the customary responses. They all recite the Amidah inaudibly. The reader repeats the Amidah aloud, as in the morning service, till he has concluded the whole of it. All then bow their heads, offering supplications; raise their heads and continue their supplications remaining seated, as in the morning service. The reader then rises and recites Kaddish. The people make the customary responses. Then they depart to their affairs.

If one has occasion to go into a synagogue to call a child or other person, he may go in, but should read some portion of Scripture or recite a traditional dictum, so that his entry shall not be for the sake of his private affairs only. If he has no knowledge he should say to one of the children, "Recite to me the verse which you are now reading" or he should stay a while in the synagogue and then leave, for staying there is also a religious act, as it is said, "Happy are they that dwell in Thy house" (Psalms 84:5).

The Laws of the Holiness of a Synagogue (containing 12 S'ifim):
In a synagogue or house of study, one may not behave frivolously; for example: laughter, sarcasm, or idle conversation. One should not eat or drink in them, nor should one groom oneself in them or strolling around in them. One should not enter them in summer due to [seeking shelter from] the sun, nor in the rainy season due to [seeking shelter from] the rain. Torah scholars and their students are permitted to eat and drink in them out of necessity. (And there are those who say that in a house of study, it is permissible even when it is not out of necessity) (Ran, [on] chapter "B'nai Ha-ir" [i.e. Talmud Megillah, Chapter 4]). No monetary calculations should be made there unless they are for the purpose of a mitzvah; for example, collecting money for tz'dakah, or for the redemption of captives. And we do not deliver eulogies in them unless would be for a eulogy for one of the prominent members of the city, for all the people assemble and come to eulogize [such a person]. If one must enter there for one's own needs; for example, to call someone - one should enter and read a little or say a word of [Torah], and after that, call [the person] so that it should not appear as if one has entered for one's own needs. And if one doesn't know how to read or repeat [e.g., a mishnah], one should say to one of the children: "recite a verse that you are learning for me", or one should delay there for a bit, and [only] after that, leave, because sitting among them is a mitzvah, as it says "praiseworthy are those who dwell in Your house". (And the amount of sitting time corresponds to [the time is takes for] walking [the width of] two doorways.) (According to the opinion of "those that explain" in siman 90 at the end of s'if 20) (Mordechai at the beginning of chapter "HaShut'fin" [Bava Batra, Chapter 1]).