Disclaimer: fellow learner, not native or fluent.
ל = to
this/that = זה
to it/to this = לזה
there is = יש
In Hebrew, possession is expressed as "to this thing there is". I see you have a reasonably high level of Russian, and to me it seems to work in a fairly similar way to у меня есть. The יש functions like есть, ל like у, and the זה is the pronoun, меня/вас/него etc. It's not a perfect comparison - in Hebrew the "to" part (equivalent to the Russian у) joins on to the pronoun, and the pronoun doesn't decline the same way (although you do have, say, אנחנו being shortened when it combines with ל, so it becomes לנו), but all told it's a pretty similar construction. And the ל can combine with a bunch of different endings to create various forms, יש לי I have (literally: to me is), יש לנו we have, יש לה she has and so on.
In this case, the thing doing the possessing is being referred to as a "that" or "it", so לזה is used.
... does that help at all?
Literally it would be something like "there is ( יש ) to- [prep. ( ל )] -it [pron. dem. sing. masc. ( זה )] nut [nomen sing. masc. indef. ( אגוז )] beautiful [adj. sing. masc. indef. (in agreement with the preceeding noun) ( יפה )]" - "there is to it a beaufiful nut". The construction יש לפ ק ("yesh l-p q") i.e. "there is to p q" is often translated in English as "p has q" which would make the translation of the entire sentence in English "it has a beautiful nut". Cf. Tips & Notes of the skill "there is" (on the left in the 5th row). - I hope this makes some sense.
What does this sentence mean? Are we talking about a piece of carpentry where the bolt is held on by a decorative fastener? About an oak tree (or maybe a squirrel) with a lovely acorn? Neither hardware nor large edible seeds are renowned for their beauty, and I can't think of any other meaning of "nut" that would make this a plausible English sentence.