Потом я взяла веник и совок, потому что на полу была земля с ботинок.

Because Russian past tense agrees with the subject in gender and number.

• я взяла = I took (said by a woman)
• я взял = I took (said by a man)
• мы взяли = we took

So взяла tells you the speaker is female.

This is an aspect question.

• взять / взяла = to take in the perfective sense: a completed, one-time action
• брать / брала = to take in the imperfective sense: process, repetition, or habitual action

Here the speaker means a single completed action in a sequence: Then I took a broom and dustpan...
That is why взяла is the natural choice.

• веник = broom
• совок = dustpan

So взяла веник и совок means took a broom and a dustpan.

A small extra note: совок can also have other meanings in different contexts, including slang, but here it very clearly means dustpan.

Because потому что introduces a subordinate clause, like because in English.

The sentence has two parts:

• Потом я взяла веник и совок
• потому что на полу была земля с ботинок

In standard Russian, a clause introduced by потому что is separated by a comma.

Because this is location, not direction.

• на полу = on the floor / on the ground → where something is
• на пол = onto the floor → movement toward a place

Here the dirt was already located there, so Russian uses на полу.

Also, пол has a special locative/prepositional form here: на полу.

Because земля is a feminine singular noun.

In the past tense, быть appears as:

• был for masculine
• была for feminine
• было for neuter
• были for plural

Since земля is feminine, it must be была земля.

Yes. Земля literally means earth, soil, ground, or land, and in this sentence it means soil/dirt tracked in from outside.

So земля с ботинок means something like:

• dirt from the boots
• soil off the boots

It is understandable and natural if actual soil was brought in.

They are similar, but not identical.

• земля = earth/soil
• грязь = dirt/mud/mess

If the boots brought in actual soil from outside, земля is a good choice.
If you want a more general idea of mud or dirt on the floor, грязь might also be possible.

So the sentence suggests specifically soil/earth from the boots.

Here с means from/off, and with that meaning it takes the genitive case.

So:

• dictionary plural: ботинки = boots
• genitive plural: ботинок

That is why you get с ботинок = from the boots / off the boots

This form can be confusing because ботинок is also the singular nominative form meaning a boot. But here the context clearly shows it is genitive plural after с.

Yes. Russian word order is fairly flexible.

• Потом я взяла... = neutral narrative: Then I took...
• Я потом взяла... = puts a little more focus on I
• Потом взяла... = possible if the subject is already clear from context

Russian often drops subject pronouns when they are obvious, but including я is also perfectly normal.

Because Russian has no articles.

English distinguishes:

• a broom
• the broom

Russian does not do this with separate words. Instead, definiteness is understood from context.

So веник, совок, полу, and ботинок do not need any article equivalent.